Kant's essay is best viewed as a polemic, directed at his king and others in authority, arguing as he does that while private use of reason can and often should be restricted, public use of reason must always be given free rein... if the goal of those in authority is that society achieve its highest potential [page 55]. By "public use of reason", Kant means that process by which the thoughts and views of learned and informed individuals are promulgated throughout society by means of scholarly writings and public discourse. He terms "private use of reason" that which a person might employ in carrying out his duties within a particular post or office to which he has been entrusted [last line, page 55].
How do these admonitions of Kant relate to his views on metaphysics, as elaborated in his Prolegomena to Any Future Metaphysics ?... And, in particular, how can its sub-discipline, religion, have the potential to become a more "enlightened" field of inquiry and endeavor over time? For Kant's present essay on "Enlightenment" to make any sense at all, vis-à-vis the possibility of there being "enlightenment in religion", it is necessary to assume that at least one of the following must be true:
A. That metaphysics, insofar as spiritual and religious matters are concerned, is a science that can make progress and become "more enlightened" over time by adding to its store of "a priori synthetic knowledge", brought about by public use of reason in scholarly discourse.
B. That human happiness and societal contentment will be enhanced through "more enlightened" forms of religious belief and practice, and will be diminished through "less enlightened forms"... and that, over time, through free public discourse based on public use of reason, the better forms of religious belief and practice will become predominant, allowing religious belief to make progress as a "social science".
C. That since "absolute truth" with respect to proper religious belief and practice can never be known, given the limits of metaphysical inquiry, the free exchange of ideas regarding religion by means of public use of reason, nonetheless, represents a desirable "end in itself"... always preferable to the maintenance of a fixed, unquestionable body of religious dogmatism. One might ask, though, whether this last position is inherently obvious... or needs to be supported by means of logically sound arguments.
In conclusion, it is noteworthy that aside from drawing the distinction between public and private uses of reason, Kant notes that, unlike in the case of public use of reason... private use of reason must often be curtailed. He states that, "a lesser degree of civil freedom gives intellectual freedom enough room to expand to its fullest content" [page 59]. In other words, one must often do one's duty as an agent of society and, in so doing, further an idea or enterprise that is in direct opposition to one's own standards of sound logic and reasonableness. For example, the editor of a newspaper or scholarly journal might have an obligation to print a well-framed article, even though he might believe that the contents of the article are false and counter-productive. By curbing his own private use of reason and allowing the article to be published, he allows the general public to see the contents and decide for itself... thereby allowing public use of reason to have its largest audience and its greatest impact.