The rapid recent expansion of copyright law worldwide has sparked efforts to defend the ‘public domain’ of non-propertized information, often on the ground that an expansive public domain is a condition of a ‘free culture’. Yet questions remain about why the public domain is worth defending, what exactly a free culture is, and what role (if any) authors’ rights might play in relation to it. From the standard liberal perspective shared by many critics of copyright expansionism, the protection of individual (...) expression by means of marketable property rights in authors’ works serves as an engine of progress towards a fully competitive ‘marketplace of ideas’ – though only if balanced by an extensive public domain from which users may draw in the exercise of their own expressivity. This article shows that a significantly different, and arguably richer, conception of what a free culture is and how authors’ rights underpin it emerges from a direct engagement with the philosophy of Immanuel Kant. For Kant, progress towards a fully emancipated (i.e. a ‘mature’ or ‘enlightened’) culture can only be achieved through the critical intellectual activity that public communication demands: individual expressive freedom is only a condition, not constitutive, of this ‘freedom to make public use of one’s reason in all matters’. The main thesis defended in this article is that when Kant’s writings on publicity (critical public debate) are read in relation to his writings on the legal organization of publishing, a necessary connection emerges between authors’ rights – as distinct from copyrights – and what Jürgen Habermas and others have named the public sphere. I conclude that it is the public sphere, and not the public domain as such, that should serve as the key reference point in any evaluation of copyright law’s role in relation to the possibility of a free culture. (shrink)