Religious Beliefs and Socialization: An Empirical Study on the Transformation of Religiosity in Spain from 1998 to 2018

Abstract

This empirical study investigates the transformation of religiosity in Spain over the two decades from 1998 to 2018, with a focus on social changes in belief, religiosity, and religious controversies, as well as the evolution of religious socialization. By incorporating the concepts of religious socialization and religious controversy into the theoretical framework, the study analyzes data from three waves of surveys on religious topics conducted in Spain during this period. The descriptive findings reveal a clear trend towards a decline in religious belief, religiosity, and practice, coupled with a significant rise in atheistic and non-religious attitudes. Moreover, the explanatory analysis indicates a reduction in the impact of primary religious socialization during childhood, while sociodemographic variables such as age and ideology have either maintained or increased their influence in shaping religious or non-religious positions. The study identifies religious polarization, driven by a marked increase in atheism and non-religion, and suggests that intergenerational and ideological shifts are more critical in explaining changes in religious beliefs than traditional religious socialization processes.

1. Introduction

Spain has historically been a country with a strong Catholic tradition. However, significant changes have been observed in recent decades. While the most common explanation for this shift is the secularization of Spanish society following the democratic transition of 1978 (Requena 2019), we argue that this transformation is more profoundly influenced by changes in values, ideology, and generational turnover.

This ideological and generational positioning is crucial for understanding the variations in religious controversies and the evolution of religious socialization, beliefs, and rituals over the two decades from 1998 to 2018. The decline in religious identity and practice is not solely attributable to secularization but is also significantly affected by shifts in social values and ideological perspectives, particularly among younger generations.

The primary objective of this research is to analyze the variations in religiosity among Spaniards over the two decades from 1998 to 2018, focusing on levels of socialization, beliefs, and rituals. Our research question explores how a society with a strong historical connection to Catholicism has experienced a decline in religious identity and what factors have been most influential in this change since the political transition of 1978.

In addition to the general secularizing trend observed in Western European societies, we believe that the variations in religious identities in Spain—shifting towards more atheistic, agnostic, or deist positions—are largely driven by factors such as increased social association, reduced religious experience or socialization, left-wing ideological leanings, and generational changes.

To investigate these trends, we will first theoretically position religious controversies and disputes over socialization, beliefs, and rituals. This will be followed by a descriptive analysis of these controversies and a multivariate study using several logistic regression models. These models will test whether ideological positioning and generational change indeed explain the observed trends in religious socialization, beliefs, and rituals in Spain.

1.1. Socialization, Beliefs, and Rituals

The concept of socialization is fundamental to the sociological understanding of the formation of human social personality, as articulated by scholars such as Mead (1968) and Cooley (1902, 1909). Socialization explains how individuals internalize societal norms, values, and traditions, which subsequently influence social organization and relationships.

In the context of contemporary Spanish society, framed within the European model of secularization, the internalization of religious convictions is significantly influenced by the socio-historical trajectory of Spaniards. This process must be understood within the relational and historical heritage of different generations. Berger (2006) posits that socialization ensures an “uninterrupted consensus about the basic characteristics of the social world”, reinforced by the legitimization of transmitted contents, especially through religion.

Despite the decline in traditional religious adherence, non-rational feelings of intergenerational group solidarity, expressed through supernatural religious beliefs, continue to persist in a significant portion of the population. According to Berger (2006), “Both religious acts and religious legitimacies, both rituals and mythologies… serve together to recall the traditional concepts embedded in culture and its major institutions. They constantly re-establish continuity between the present moment and societal tradition, placing the experiences of each individual and of the various groups that make up society within the context of a history, fictional or not, that transcends them”.

Berger further elaborates on the concept of plausibility structures, which are the real social bases taken for granted for the continuation of societies. Applied to any faith and religious institution, these structures are internalized by successive generations through the process of socialization, rendering them as real. Discontinuities in these plausibility structures over time create uncertainties or gaps in this perceived truth, which are evident in both faith and religious institutions. The Spanish reality seems to follow this pattern in the decades analyzed.

Beliefs, which are integral to the material transmitted and internalized through socialization, require strong social support for their maintenance, as noted by Brown (1962). Ideals, including religious ideals, have been analyzed from various theoretical perspectives, including philosophical and sociological approaches (Sigelman 1977; Ellis et al. 2018; Koenig 2018).

From a philosophical standpoint, certainties have been examined in relation to experience, faith, and reason (Green 1978; Alston 1982; Peterson et al. 2008). In Spain, Ortega y Gasset (1983, 1995, 1996) argued that each era or country is characterized by a specific belief base, which, although varying over time, maintains the same mode of belief and internalization: the acceptance of reality as an assumption. Fustel de Coulanges (2006, p. 284) illustrated this with the transformation of beliefs in ancient Greece and Rome: “When then, the beliefs on which this social regime rested weakened, as soon as the majority of men’s interests found themselves at variance with such a regime, it had to succumb. No society has been exempted from this law of transformation”.

Ortega y Gasset (1996) distinguishes between two kinds of beliefs: one that is a simple assertion appearing in the mind, and another that is reasoned, supported by a motive or foundation. The former, associated with religion, habit, and tradition, is believed irrationally and blindly, while the latter, akin to scientific belief, is motivated and rational.

Sociologically, certainties, rites, and cults—collectively understood as religion—constitute the essence of the idea of society (Durkheim 1968). These are specific experiences manifesting differently across societies. Weber (1999) noted that in the United States, religious beliefs or affiliations are closely tied to social, commercial, and credit life. He also observed that, aside from Christianity and other ascetic faiths, ancient religious beliefs were often anchored in health, long life, and wealth. Weber (1998) further described belief systems as theodicies, frameworks that construct the world as meaningful, providing explanations for fundamental questions like predestination.

Religions encompass not only dogmas but also the practice of these dogmas through rituals or worship (Durkheim 1968). Rites, as religious acts repeated periodically within a society or cultural community, reflect the society’s cosmology or religious ideas. Durkheim posited that rites are the initial germ of religious life and an essential external sign of the recognition of the religious phenomenon, providing insights into the level of religious conviction within a given society.

By examining these sociological and philosophical frameworks, this study aims to provide a comprehensive understanding of the transformations in religiosity in Spain over the two decades from 1998 to 2018, contextualizing these changes within broader theoretical perspectives.

1.2. Religious Controversies

As previously discussed, while beliefs have consistently existed throughout history, their specific convictions have evolved across different societies and eras. This is particularly evident in the realm of religious controversies, which have shifted significantly over time.

The historical trajectory of religious thought in Western culture begins in pre-Socratic Greece and continues to the present day, heavily influenced by the Enlightenment of the 18th century. Greek deists like Anaxagoras (Cicero 2015) laid the early groundwork, which was later expanded by Enlightenment thinkers such as Voltaire (2021) and Hume (2010, 2014), and more recently by Kauffman (2008). Skeptics and agnostics, including Cicero (2015), Huxley (1889b), Clifford and James (2003), and Santayana (2015), have also contributed to this discourse. Meanwhile, atheism, championed by figures such as Diagoras of Melos, Theodore of Cyrene (Cicero 2015), Holbach (2016), Shelley (2015), Mill (2014), Russell (1979), Dawkins (2006), and Sartre (2006), offers a distinct perspective.

The differentiation between deists, agnostics, skeptics, and atheists was clearer historically, even though it might be more nuanced today. Deism, for instance, first appeared in pre-Socratic Greece, with Anaxagoras positing that the universe’s orderly arrangement was the result of a rational, infinite mind (Cicero 2015). This laid the foundation for subsequent philosophical debates on skepticism, agnosticism, and atheism, where Protagoras expressed doubt, and Diagoras of Melos and Theodore of Cyrene outright denied the existence of gods (Cicero 2015).

The social, legal, political, and military structures of ancient Greece and Rome were deeply rooted in religious beliefs, both familial and public (Fustel de Coulanges 2006). During the Enlightenment, thinkers like Hume advocated for deism, suggesting that the natural world’s order indicated an intelligent designer (Hume 2010, 2014). Voltaire echoed this sentiment, asserting that true religion entails worshiping God and fostering goodness, a belief he deemed incapable of producing evil (Maurois 1938). Kauffman (2008) further expanded on deism, describing a natural God inherent in the universe’s creativity.

Skeptical and agnostic positions, introduced by Cicero, argued that while multiple philosophical opinions might exist, it is improbable that more than one is true (Cicero 2015). Huxley (1889a), a proponent of agnosticism, suggested that logic should guide one’s conclusions, dismissing unproven claims. Clifford and James (2003) emphasized that believing something without sufficient evidence is inherently flawed, while Santayana (2015) viewed agnosticism as holding epistemological value.

Atheism, grounded in reason and empirical knowledge, critiques superstition and religious beliefs (Holbach 2016; Shelley 2015). Mill (1989, 2014) and Sartre (2006) highlighted atheism’s reliance on human reality and social influence. Over time, atheism has evolved into various forms, from friendly atheism (Martin 1990) to militant atheism (Savater 1990), and movements like new atheism (Dawkins et al. 2019) and combative atheism (Harris 2005), which advocate for the rational critique and opposition of religion.

The transition from theism, agnosticism, and atheism to Christianity reflects a decline in intolerance from the 19th century onwards, driven by common sense and science (Mill 2014). Believers justify their faith through intergenerational traditions and scientific exceptionality. Pascal (1998) contended that faith transcends sensory perception without contradicting it, a view shared by enlightened Catholics like Von Haller (1760) and Euler (1768), who saw no conflict between religion and science, but rather between reason and the eudaimonistic practices of atheism. Haller argued that wisdom centered solely on individual sensual happiness undermines social life (Von Haller 1760). This perspective persists today (Lyden 1995), with James (2003) legitimizing faith through voluntary acceptance, and Ratzinger (2006) emphasizing religion as an experiential reality beyond pure rationality.

Durkheim (1968) and Weber (1999) both addressed the relationship between religious and scientific thought, asserting that religious beliefs are based on specific experiences with demonstrative value, different yet not inferior to scientific experiences. Religion, according to Weber (1999), offers an immediate understanding of the world’s meaning rather than an intellectual knowledge of its nature.

In refining our theoretical framework, we integrated and restructured this section to avoid a mere aggregation of theories and opinions, aiming instead to provide a nuanced analysis that illuminates the complex dynamics of contemporary religiosity in Spain. This allows us to establish clear connections between the empirical categories and the philosophical and theoretical positions explored.

Focusing on secularization and its interaction with religious and spiritual forms in modern Spain, we draw on Charles Taylor’s “A Secular Age” (2007) to illustrate how Spanish society reflects a scenario where the sacred and the secular coexist and intertwine in significant ways. This approach helps us understand religiosity as a spectrum of evolving experiences and practices.

By examining deism, agnosticism, skepticism, and atheism as manifestations of a continuum of religious understanding shaped by socio-cultural and generational changes, we build on Berger’s (2014) concept of religion as a socially negotiated construct. This framework allows us to explore how various forms of religiosity and non-religiosity materialize in individual and collective experiences within Spanish society.

2. Materials and Methods

The primary objective of this research is to analyze the variations in religiosity experienced by Spaniards in their levels of socialization, beliefs, and rituals from 1998 to 2018, with a focus on different religious controversies.

The specific objectives of this study are threefold:

• To describe and analyze changes in religious belief and identity among Spaniards over the past two decades.
• To examine the transformations in religious socialization and practices and their impact on various religious disputes.
• To utilize logistic regression models to determine whether ideological identification, generational change, and other socio-demographic variables, as well as religiosity, socialization, and religious practices, satisfactorily explain the trends in religious beliefs in Spain.

Our working hypothesis posits that, although Spain has historically been characterized by predominantly Catholic religious socialization, the past decade has seen a significant shift towards more atheistic, agnostic, and skeptical positions due to ideological and generational changes.

For this analysis, we utilized data from the Centro de Investigaciones Sociológicas (CIS), specifically three waves of the International Social Survey Programme (ISSP) on Religion. The ISSP is a cross-national collaborative program that conducts annual surveys on various social science topics (Fernández-Prados et al. 2019). The data for our study were sourced from the following surveys:

• Religion I (survey No. 2301), conducted in September 1998.
• Religion II (survey No. 2776), conducted from October to November 2008.
• Religion III (survey No. 3194), conducted from October 2017 to January 2018 (Smith and Schapiro 2021).

Although the sample size of the third survey was somewhat smaller, resulting in a higher sampling error, the methodological guidelines and technical specifications across the studies remained consistent (see

Table 1. Technical Characteristics of ISSP Surveys on Religion in Spain (1998–2018).

	Religion I (1998)	Religion II (2008)	Religion III (2018)
Population	Residents in Spain aged 18 and over	Residents in Spain aged 18 and over	Residents in Spain aged 18 and over
Sample	2488 (personal interviews)	2768 (personal interviews)	1733 (personal interviews)
Sampling error	±2%	±1.9%	±2.4%
Level of Confidence	95.5% (two sigma), P = Q	95.5% (two sigma), P = Q	95.5% (two sigma), P = Q

Source: Own elaboration. CIS.

).

In our methodology, we integrate the perspectives of Casanova (2012) and Berger (2014) to move beyond the traditional secularization narrative in Spain. This approach allows us to focus on the complex interplay between the secular and the sacred, as well as the diversification of religious forms in modernity. By adopting this framework, we aim to enhance our understanding of the evolution of religiosity in Spain, emphasizing the plurality and dynamic nature of religious beliefs and practices in the 21st century.

This study employs a multi-faceted analytical approach to examine the evolution of religiosity in Spain over two decades. For the first three sections of our results (Analysis of Beliefs and Religiosity, Evolution of Religious Controversies, and Religious Socialisation and Its Impact), we utilize descriptive statistics, trend analysis, and comparative statistics. Specifically, we employ frequency distributions and cross-tabulations to examine changes in religious beliefs and self-reported religiosity over time. Chi-square tests are used to assess the relationship between parental religiosity and individual beliefs, providing insights into the impact of religious socialization. These analyses offer a comprehensive overview of the changing religious landscape in Spain and the evolving dynamics of various religious positions.

For the final section of our results (Evolution of explanations for belief in God: between socio-demographic and religious socialisation variables), we employ logistic regression models. These models are constructed for each of the three time points (1998, 2008, and 2018) to examine how the influence of various socio-demographic and religious socialization factors on belief in God has changed over time. To ensure the robustness of our findings, we conduct multicollinearity tests using the correlation matrix for each time point (Tabachnick and Fidell 2019). The dependent variable ‘Belief in God’ is dichotomously coded, while independent variables include both categorical and continuous measures. The Hosmer–Lemeshow test is used to assess the goodness of fit for each model, and Nagelkerke’s R² is calculated to measure the models’ explanatory power. This rigorous approach allows us to identify significant predictors of religious belief and how their influence has evolved over the two decades under study.

3. Results

3.1. Analysis of Beliefs and Religiosity

The survey questions addressing beliefs were broad, encompassing an assessment of religious change and the respondent’s religious identity or degree of spirituality. These questions were consistent across the three surveys, focusing on belief in God and the degree of religiosity.

In all three questionnaires, the following questions were maintained:

Belief in God: Q. 19 (1998); Q. 17 (2008); Q. 43 (2018): “Of the following statements, Which best describes your beliefs about God?

• I don’t believe in God now and I never have
• I don’t believe in God now, but I used to
• I believe in God now, but I didn’t used to
• I believe in God now and I always have
• Can’t choose

For analysis purposes, options one and two were grouped as “Do not believe in God”, and options three and four as “Believe in God”.

Degree of Religiosity: Q. 33 (1998); Q. 31 (2008); Q. 58 (2018): “Would you describe yourself as…?

• Extremely religious
• Very religious
• Somewhat religious
• Neither religious nor non-religious
• Somewhat non-religious
• Very non-religious
• Extremely non-religious
• Can’t choose

For the analysis, options 1 and 2 were categorized as “Very religious”; options 3 and 5 as “Somewhat or not very religious”; option 6 as “Not religious at all”; and option 7 as “Extremely non-religious”. Option 5 was excluded due to its ambiguity.

Over the past two decades, belief in God has remained prevalent among the Spanish population, although it has declined significantly from 83% in 1998 to 64.6% in 2018. The most notable decrease occurred among those who have always believed in God, which dropped by 18.5%, particularly in the last decade. Conversely, those who previously believed in God but now do not increased by 10.7%, effectively doubling in absolute numbers. Additionally, those who have never believed in God increased by 6.8%, while those who believe in God now but did not before saw a slight increase of one percentage point.

Regarding trends in religiosity, a similar pattern to belief in God is observed. While the majority of Spaniards identified as religious, this number decreased by approximately 12 percentage points from 81.7% in 1998 to 64.6% in 2018. The most significant changes were among the very religious and the extremely non-religious, with the former group halving from 16.4% in 1998 to 8.6% in 2018, and the latter group increasing nearly fourfold from 3.5% to 13.2% over the same period (see

Table 2. Religious identity: Belief in God and Religiosity.

Belief in God	1998	2008	2018	Variation 1998–2008	Variation 2008–2018	Variation 1998–2018
I don’t believe in God now and I never have	9.0	9.1	15.8	0.1	6.7	6.8
I don’t believe in God now, but I used to	8.9	15.5	19.6	6.6	4.1	10.7
Total “Does not believe in God”	17.9	24.6	35.4	6.7	10.8	17.5
I believe in God now, but I didn’t used to	1.8	2.0	2.8	0.2	0.8	1.0
I believe in God now and I always have	80.3	73.4	61.8	−7.0	−11.6	−18.5
Total “Believe in God”	82.1	75.4	64.6	−6.7	−10.8	−17.5
Religiosity	1998	2008	2018	Variation 1998–2008	Variation 2008–2018	Variation 1998–2018
Extremely non-religious	3.5	8.0	13.2	4.5	5.2	9.7
Not religious	14.8	11.3	17.3	−3.5	6.0	2.5
Total “Non-religious”	18.3	19.4	30.5	1.1	11.2	12.2
Somewhat-Little Religious	65.3	69.2	60.9	3.9	−8.3	−4.4
Very Religious	16.4	11.5	8.6	−4.9	−2.9	−7.8
TOTAL “Religious”	81.7	80.6	69.5	−1.1	−11.2	−12.2

Source: Own elaboration. CIS.

).

These trends indicate a decline in belief in God and religiosity, with a more pronounced increase in the number of never-believers and those who are extremely non-religious.

3.2. Evolution of Religious Controversies

The diverse religious controversies presented in this study reflect a wide range of sentiments regarding belief in God, encompassing atheists, believers, agnostics, deists, skeptics, and doubting believers. The survey results indicate a significant decline in believers, with their proportion dropping by 15.2 percentage points—from 45.8% in 1998 to just 30.6% in 2018. In contrast, atheists represent the fastest-growing group over the two decades, doubling from 8.6% to 17%. Over the last ten years, atheists have shown a significant increase of 7.2 percentage points, making them the only group with a marked increase. Other groups, such as deists and skeptics, have either remained stable or shown only slight growth, while agnostics experienced a notable increase primarily in the first decade.

The questions related to religious controversy, which served as the dependent variable in the research, remained consistent across all three waves of the survey: Q. 18 (1998); Q. 16 (2008); Q. 42 (2018): “Please indicate which statement below comes closest to expressing what you believe about God:

• I don’t believe in God.
• I don’t know whether there is a God and I don’t believe there is any way to find out.
• I don’t believe in a personal God, but do believe in a Higher Power of some kind.
• I find myself believing in God some of the time, but not at others.
• While I have doubts, I feel that I do believe in God.
• I know that God really exists and I have no doubts about it.
• Can’t Choose
• No Answer

For clarity, these responses were recoded into categories: Category 1 as “atheists”, category 2 as “agnostics”, category 3 as “deists”, categories 4 and 5 as “believer-skeptics”, and category 6 as “believers”.

The trends for the current decade suggest that the percentages of atheists and believers are now roughly equal, each constituting about a quarter of the population (see

Table 3. Evolution of religious controversies in 1998, 2008 and 2018.

	1998	2008	2018	Variation 1998–2008	Variation 2008–2018	Variation 1998–2018
Atheists	8.6	9.8	17.0	1.2	7.2	8.4
Agnostic	6.9	10.5	11.3	3.6	0.8	4.4
Deist	12.4	12.1	11.8	−0.3	−0.3	−0.7
Sometimes believer or sceptic	7.3	8.5	9.1	1.2	0.6	1.8
Believer with doubts	18.9	20.4	20.2	1.5	−0.2	1.2
Believer	45.8	38.8	30.6	−7.0	−8.2	−15.2

Source: Own elaboration. CIS.

). The remaining options include believers with doubts and about ten percent of skeptics, with similar proportions of deists and agnostics.

These findings provide a nuanced understanding of the shifts in religious beliefs and controversies in Spain, highlighting the dynamic interplay between belief, skepticism, and non-belief over the last two decades.

3.3. Religious Socialisation and Its Impact

The process of received and internalised socialisation, specifically religious socialisation, significantly influences the opinions, attitudes, ideas, and beliefs of Spaniards. The surveys collected information on the religiosity of parents and their religious practices during the childhood years of the interviewees.

The data show that most Spaniards had religious parents during their childhood (see

Table 4. Evolution of religious controversies in 1998, 2008 and 2018.

	Maternal Religiosity			Paternal Religiosity
	1998	2008	2018	1998	2008	2018
Atheists	84.4	88.2	82.2	72.8	79.8	74.6
Agnostic	92.2	92.7	91.1	84.0	87.3	84.7
Deist	97.6	96.1	94.0	94.5	85.8	85.4
Sometimes believer or sceptic	98.3	98.5	93.6	93.2	94.9	90.3
Believer with doubts	98.9	99.2	98.0	94.7	95.0	95.0
Believer	99.6	99.6	99.8	97.2	96.2	97.1
Total	97.4	97.1	94.2	93.1	92.1	89.5

Source: Own elaboration. CIS.

). The religiosity of mothers exceeded 90% in all survey waves, while the religiosity of fathers also remained high, though slightly lower in the last survey of 2018. There was a small decrease over the two decades, about three and four percentage points for mothers and fathers, respectively. Notably, there are significant differences in parental religiosity between respondents who declared themselves atheists and those who identified as believers, with around three-quarters of respondents who declared as atheists having religious parents, compared to almost one hundred percent of believers.

Regarding the frequency of attendance at religious events at least two or three times a month, a downward trend persists over the two decades analyzed. The most frequent religious practice corresponds to the interviewees themselves during their childhood, followed by the mother, and finally the father (see

Table 5. Religious socialisation: Parents’ religious practice. childhood and current in 1998, 2008 and 2018.

	Maternal Religious Practice			Paternal Religious Practice
	1998	2008	2018	1998	2008	2018
Atheists	44.7	38.0	35.0	24.0	18.7	16.7
Agnostic	51.0	43.2	48.1	34.4	29.6.	30.6
Deist	55.0	47.6	45.7	37.0	25.7	25.3
Sometimes believer or sceptic	58.4	56.4	50.3	31.9	37.8	31.4
Believer with doubts	64.1	61.7	60.1	40.3	40.7	36.4
Believer	77.3	71.8	72.3	54.0	53.3	54.7
Total	66.2	59.2	55.6	43.8	40.1	36.2
	Religious Practice in Childhood			Religious Practice Today
	1998	2008	2018	1998	2008	2018
Atheists	38.4	44.1	35.4	2.8	0.4	1.1
Agnostic	53.0	54.9	46.6	2.9	2.5	3.1
Deist	63.3	58.7	51.0	12.1	5.0	3.5
Sometimes believer or sceptic.	69.4	61.8	56.1	14.4	9.7	7.0
Believer with doubts	74.0	73.6	68.7	28.5	16.9	18.0
Believer	84.0	79.8	80.0	47.0	40.5	43.1
Total	72.5	68.3	60.8	29.9	20.8	18.4

Source: Own elaboration. CIS.

). The majority of the first two categories remained the same, while the fathers’ participation accounted for barely a third. Notably, believers had more than twice the number of religious events in their childhood (over 80% for interviewees and over 70% for mothers) compared to atheists (35% for interviewees and mothers). The decline in religious practice is more severe for the respondents themselves throughout their childhood, with about 12 percentage points lost over the two decades, 11 points for mothers, and about 7.5 points for fathers.

These tables provide a comprehensive overview of the evolution of religious socialisation and practice in Spain over the past two decades. The decline in religiosity and religious practice among Spaniards indicates significant shifts in societal values and generational changes, contributing to the broader trends of secularisation.

3.4. Evolution of Explanations for Belief in God: Between Socio-Demographic and Religious Socialisation Variables

Beyond the descriptive and comparative analysis of trends in beliefs, religiosity, and socialisation, a multivariate analysis provides an explanatory approach to the variables influencing belief in God in Spain. To this end, logistic regression analyses were conducted for each survey wave (1998, 2008, and 2018). The dependent variable was dichotomous, representing belief in God or lack thereof. Independent variables included: sex (dichotomous: 0 = Male, 1 = Female), age (continuous), education level (ordinal), socioeconomic status (ordinal), ideology (scale from 1 to 10, where 1 represents extreme left and 10 extreme right), parental religiosity (dichotomous: 0 = No, 1 = Yes), and religious practices of the mother, father, and the respondent during childhood (ordinal frequency scale). To assess the validity of the model, multicollinearity tests were performed using the correlation matrix. No correlations exceeding 0.8 were observed among the independent variables across the three analyzed periods (1998, 2008, and 2018), indicating the absence of severe multicollinearity issues. The highest correlation observed was 0.557 between education level and socioeconomic status in 2008. The model’s goodness of fit was evaluated using the Hosmer–Lemeshow test. Results for the three periods were as follows: 1998 (χ²(8) = 5.165, p = 0.740), 2008 (χ²(8) = 15.526, p = 0.050), and 2018 (χ²(8) = 13.502, p = 0.096). These findings indicate an acceptable model fit to the data across all three periods. The variable selection procedure followed the “intro” method, where all variables in a block are introduced simultaneously. This resulted in three logistic regression models, each with a moderately high and consistent explanatory power, as indicated by Cox and Snell’s R-squared values exceeding 20% across all three waves. The results highlight the independent variables that significantly contribute to the explanatory power of each model, with significant variables marked in bold (see

Table 6. Logistic regression analysis of Belief in God according to socio-demographic and religious socialisation variables 1998, 2008 and 2018.

	1998			2008			2018
	B	Sig.	Exp(B)	B	Sig.	Exp(B)	B	Sig.	Exp(B)
Sex (1)	−0.896	0.000	0.408	−0.601	0.000	0.548	−0.610	0.000	0.544
Age	0.019	0.001	1.019	0.022	0.000	1.023	0.021	0.000	1.021
Studies	−0.180	0.000	0.835	−0.251	0.000	0.778	−0.203	0.000	0.817
Socio-economic status	0.095	0.258	1.100	0.071	0.245	1.073	0.093	0.120	1.098
Ideological scale	0.391	0.000	1.478	0.343	0.000	1.409	0.311	0.000	1.364
Religious mother	−1.145	0.024	0.318	−0.742	0.059	0.476	−0.805	0.060	0.447
Religious father	−1.260	0.000	0.284	−0.305	0.209	0.737	−0.962	0.001	0.382
Religious practice (mother)	0.172	0.000	1.187	0.097	0.005	1.102	−0.008	0.816	0.992
Religious practice (father)	−0.018	0.689	0.982	0.075	0.024	1.078	0.049	0.148	1.051
Religious practice (childhood)	0.158	0.000	1.171	0.067	0.032	1.070	0.115	0.001	1.121
Constant	−1.553	0.000	0.212	−1.813	0.000	0.163	−1.527	0.002	0.217
Cox and Snell R-squared	26.2			20.9			23.7
R square of Nagelkerke	41.4			29.7			32.2

Source: Own elaboration. CIS.

).

In the 1998 wave, eight variables were significant, in 2008, seven variables were significant, and in 2018, six variables were significant. Notably, four out of five socio-demographic variables remained highly significant (p < 0.001) across all three models. These variables included gender (being female), age (being older), education (lower levels), and ideology (right-wing), while socioeconomic status did not maintain significance. Among the religious socialisation variables, only religious practice during childhood remained consistently significant across all three waves. The significance of other variables related to parental religiosity and practice diminished over time.

These results indicate that socio-demographic variables such as gender, age, education, and ideology play a more significant role in explaining belief in God than variables related to religious socialisation. The diminishing significance of parental religiosity and practice over time suggests that generational and ideological factors increasingly influence religious beliefs in Spain.

4. Discussion

The trajectory of religiosity in Spain, traditionally a predominantly Catholic country, is undergoing significant transformation. The data from our surveys suggest that while religiosity and belief in God remain prevalent, there is a marked decline in religious practice. This decline is more pronounced in the latter two decades analyzed, indicating a shift towards secularisation in line with broader Western European trends, albeit with specific Spanish characteristics.

The descriptive analysis reveals a substantial increase in the number of individuals identifying as atheists, paralleled by a decrease in those identifying as believers. This trend is indicative of a polarisation within the Spanish religious landscape, with a growing segment of the population moving towards atheism and extreme non-religiosity. The decline in believers is particularly stark among those who have always believed in God, suggesting a generational shift in religious identity and practice.

Our explanatory analysis, using logistic regression models, highlights the decreasing influence of traditional religious socialisation factors, such as parental religiosity and religious practices during childhood. Instead, socio-demographic variables, particularly gender, age, education, and ideology, have become more significant predictors of belief in God. The data show that being male, young, highly educated, and left-wing is associated with non-belief in God, while being female, older, less educated, and right-wing is associated with belief in God.

These findings are consistent with studies from other countries, which also highlight the generational and ideological dimensions of religious change (Molteni and Biolcati 2023; Majo 2022). For instance, research in Catholic Portugal shows similar trends toward secularisation and the diversification of religious identities (Coutinho 2023).

The works of Gray (2002) and Onfray (2005) offer critical perspectives on the growing scepticism and atheism in contemporary society, challenging traditional religious conceptions. These contributions help us understand the complex interplay between secularisation and religiosity in Spain, depicting a landscape where religious practices and beliefs are continually evolving. This study underscores the importance of recognising the plurality of discourses on religion and secularisation, thereby providing a more nuanced understanding of Spanish religiosity in the 21st century.

Recent empirical evidence on the evolution of religiosity in Spain underscores the complexity of the secularization phenomenon and the crucial importance of sociodemographic variables in this process. Studies by Molteni and Biolcati (2023) and Rosa-González and Cabrera (2023a, 2023b) corroborate our findings on the general decline in religious identification, while adding important nuances. The generational cohort effect appears to be more determinant than age or period effects, suggesting that religious decline is primarily due to demographic replacement. Furthermore, factors such as urbanization, educational level, and regional differences significantly modulate this process. The persistent, albeit possibly decreasing, gender gap in religiosity and the marked variations between urban and rural areas indicate that secularization in Spain is not a uniform phenomenon, but rather deeply intertwined with broader social changes. These findings emphasize the need for a multidimensional approach to understanding the evolution of religious beliefs in the contemporary Spanish context.

It is important to acknowledge certain limitations of this study. While the logistic regression model provides a robust approximation of factors influencing belief in God, the complex nature of religiosity implies that other factors not captured in this analysis may exist. Furthermore, the decline in the model’s explanatory power over time suggests that new factors relevant to understanding religiosity in contemporary Spain may be emerging. Future research could explore additional variables and employ mixed methods to capture more nuanced aspects of the evolution of religious beliefs.

5. Conclusions

The findings of this study indicate that Spain’s religious landscape is undergoing significant transformation. While religiosity and belief in God remain prevalent, there is a notable decline in religious practice, particularly among younger generations. This decline is accompanied by an increase in atheism and extreme non-religiosity, reflecting broader secularisation trends observed in Western Europe.

The explanatory analysis highlights the diminishing role of traditional religious socialisation in favour of socio-demographic variables such as gender, age, education, and ideology. These factors are increasingly influential in shaping religious beliefs, suggesting a shift toward more individualistic and ideologically driven understandings of religion.

Future research should continue to explore the interplay between socio-demographic variables and religious beliefs, particularly in the context of broader societal changes. Comparative studies with other countries experiencing similar trends could provide deeper insights into the mechanisms driving secularisation and religious diversification.

By recognising the plurality of religious and secular discourses, this study contributes to a more nuanced understanding of Spanish religiosity in the 21st century, highlighting the ongoing evolution of religious practices and beliefs in a diverse and changing society.