In the broadly construed Western world, the advancement of secularism seems to have become a fact. According to intellectual historians and philosophers, this fact has been brought about by a variety of factors and conditions, some of which can be traced back to the early modern era, and especially to the Enlightenment. The term “secularism,” though, which originates from the Latin saeculum, has a number of different meanings, used (and sometimes abused) both in the public discourse and philosophical literature. Politically, secularism means separation of religion from the institutions of public life, such that the laws established and enforced by these institutions do not have a theological grounding or do not express preference for particular religious doctrines.  The separation of religion and political power may also imply that the state is obliged to guarantee and respect individuals’ right to confess and practice whatever creed they deem best suited to realize their striving for the (supernatural) good, but also their right to deny faith in any transcendent or supernatural reality, and act according to such convictions.
Apart from the political understanding of secularism, there is also the understanding that takes into account the historical processes as well as philosophical and ideological developments that led to the situation in which the influence of religion on society and individuals’ lives would be challenged or even marginalized.  On this construal, living in a secular society means living in a society whose members do not consider religion an important value guiding their lives, or do not abide by the doctrines, principles, and traditions of any particular faith, even though they may occasionally consider themselves believers in a transcendent God or other supernatural reality.  A secular society does not have to be one in which everyone is atheist; rather, as Charles Taylor has pointed out, it is one in which being a consistent believer has become problematic.  Without certain historical and philosophical developments – such as the Protestant Reformation, the 17 th-century wars of religion, the attempts at rationalizing revealed religion by radical reformers or enlighteners, the Enlightenment criticism of religious institutions, pleas for religious toleration and freedom of thought and speech, and the French Revolution (to name but a few) – religion would most probably have a different role to play in our social imaginary nowadays.
It should be emphasised, though, that secularism does not have to be conceived of as inimical to religion. Within what Taylor has called an “immanent frame” – which provides a context for understanding human existence and social practice without relating them to a transcendent order  – there is a possibility of an open perspective in which faith can play a due role in individuals’ lives. Still, this means that faith is one among many options in our culture nowadays, and the choice to stay in (a particular) faith requires justification. But, in political terms, secularism can as much as support religion in that it guarantees, apart from the separation of religious institutions and political power, freedom to exercise one’s beliefs, and protects freedom of conscience. In an essay written by Taylor together with Jocelyn Maclure, Secularism and Freedom of Conscience, this kind of secularism – marked by the state’s readiness to grant accommodations to citizens whenever a conflict between convictions of conscience and legal requirements occurs – is called “pluralist liberal” and opposed to the “republican” kind of secularism aiming at the relegation of religion from the public sphere. 
Finally, and perhaps most controversially, secularism and religion may even go hand in hand: this can at least be the case, according to some authors, with Christianity – to the extent that certain values foundational for a secular and liberal state originate from it. In a sense, the Christian religion can be regarded as providing an ideological basis to a secular state, for example by promoting free will and moral choice, and the conception of human beings as individual persons;  or as encouraging the development towards secularism by allowing of the rationalization of its own moral doctrines: a process to which 18 th-century thinkers, including Immanuel Kant, have significantly contributed. 
The articles collected in this special issue explore, in an original way, the intricate relations between secularism, in the diverse meanings of the term, and Enlightenment. This is not to say that the link between Enlightenment and secularism is self-evident: some have argued that attributing a secularizing tendency to the intellectual developments witnessed in the “age of reason” is anachronistic and manifests an attempt to interpret history from the point of view of only one among many competitive philosophical-historical stances,  and others have claimed that this tendency was characteristic of the “radical” as opposed to the “moderate” current of the Enlightenment thought.  However, what seems rather undisputed is the fact that particularly in the Enlightenment religion, as well as the relations between the divine and the political, became one of the key problems widely debated by the intellectuals and leading thinkers of the era. This volume offers a closer look at some of these debates which continue to bear much relevance to contemporary issues.
Accordingly, Sorin Baiasu offers an argument in support of a limited version of political secularism – understood in terms of the separation between religion and the state – that can be derived from the writings of Kant, by many scholars considered a “founding father” of secularism. The argument is based on an epistemic distinction between political and religious claims, which states that we can have moral (practical) but not religious cognition. Whereas, on Kantian tenets, faith may rest at most on subjectively sufficient grounds, knowledge – also that which pertains to our moral obligations – requires objectively sufficient justifications. Since religious claims cannot be considered knowledge claims, they cannot be held universally true, and this, one can surmise, would open up a space for a plurality of different creeds within a political community, thus for religious pluralism.
Relatedly, Mehmet Ruhi Demiray discusses Kant’s model of the relations between law, ethics, and religion against a background of the debate on whether religion can provide reasons for political-legal norms, in which two approaches prevail: austere secularism, on the one hand, and integrationism, on the other. On the basis of Religion within the Boundaries of Mere Reason, Demiray argues that, on Kant’s position, both the separation between religion and the state and the public significance of religion can be vindicated. Kant’s argument for secularism is based on his recognition of the differences between ethical and political community: the authority of the former is binding only for those who consent to it, the latter can use coercion against those who do not obey its laws. According to Kant, we have a duty to join the ethical community, and this assumes the form of a “visible church.” Thus, it is the church that provides a way to “insert” morality into the world. On this reading, religion, with its institutions, endows the ethical community with a public character and so with the state it should create a “tandem.”
Hasse Hämäläinen’s contribution also deals with ethics; it discusses the critique of “religious moral teaching” – a teaching outdated and incompatible with the modern science – advanced by the 18 th-century French philosophes: J.J. Rousseau, D. Diderot, J.C. Helvétius, and P.H. Thiry, Baron d’Holbach. In particular, Hämäläinen claims that from the works of d’Holbach one can derive a model of a non-theistic ethics with materialist underpinnings, which does not imply psychological hedonism, and thereby he undermines the dominant interpretation of the French thinker. On this reading, d’Holbach’s moral theory offers a secular justification of virtue which becomes grounded in the human striving for self-preservation, rather than in the desire of pleasure. In this light, d’Holbach can be considered an advocate of virtuous egoism.
Returning to Kant, Stephen Palmquist focuses on the Third Piece of Religion within the Boundaries of Mere Reason (which he renders as Religion within the Bounds of Bare Reason). On Palmquist’s reading, Kant’s views on the relation between religion and politics result in the model of a “non-coercive theocracy.” It is a theocracy since the ethical community – which human beings working towards their moral improvement have a duty to join – can become real only insofar as it assumes the form of a church (or a religious organization). It is non-coercive since, by definition, morality cannot be externally imposed. In this way, Kant’s model of theocracy differs from the historical forms of theocracy, such as the ancient Jewish state. Moreover, by comparing the church to a family, whose members are bound together by the law of love and thus treat one another as equals, Kant sketches a picture of an ethical community which, unlike a political community, has the potential to realize the good on earth.
Aaron Szymkowiak contributes an analysis of the views of David Hume on religion who, despite enjoying a reputation of an atheist and critic of religion, supported the policy of church establishment. One of the explanations of Hume’s surprising position is that he perceived the established church as a means of containing religious fanaticism (enthusiasm). Szymkowiak compares Hume’s position with that of Adam Smith, Hume’s critic. Smith advocates religious liberty as he believes that the free “market of sects,” i.e. competition between different denominations, provides a better means of managing enthusiasm, a development which, as Szymkowiak notes, would constitute a stage in the process of the secularization of society.
The article by Geert Van Eekert deals with an issue that is closely linked to secularism and the values it promotes – such as the liberty of conscience and religious toleration – namely, freedom of speech. Featuring early modern conceptions of free speech (by J. Locke, B. Spinoza, and J.S. Mill), and especially the Kantian account of the public use of reason, Van Eekert draws a distinction between the Enlightenment idea of free speech and the contemporary individualistic idea of free self-expression. The crucial difference between them consists in the fact that whereas the early modern and Enlightenment accounts construed free speech as a means to develop or defend a common good or value, e.g. truth, safety, justice, peace, democracy, etc., nowadays the aim of free speech is to enable an individual to be “fully oneself.” Thus, it seems that we have departed from Kant’s understanding of freedom of thought as grounded in the recognition that reason constitutes the “touchstone of truth” – insofar as it allows that its tenets be reflected upon and criticized, which, according to Van Eekert, should engage a community of rational individuals.