To become a morally good human being it is not enough simply to let the germ of the good which lies in our species develop unhindered; there is in us an active and opposing cause of evil which is also to be combatted. It was especially the Stoics who among the ancient moralists called attention to this through their watchword virtue, which designates courage and valor (in Greek as well as in Latin) and hence presupposes the presence of an enemy. In this respect the name virtue is a glorious one, and the fact that people have often boastfully misused and derided it (as of late the word “Enlightenment”) can do it no harm. – For to require courage is already halfway to instilling it; whereas the lazy and timid way of thinking (in morality and religion), which has not the least trust in itself and waits for external help, unharnesses all the forces of a human being and renders him unworthy even of this help.

However, those valiant men [the Stoics] mistook their enemy, who is not to be sought in the natural inclinations, which merely lack discipline and openly display themselves unconcealed to everyone's consciousness, but is rather as it were an invisible enemy, one who hides behind reason and hence all the more dangerous. They send forth wisdom against folly, which lets itself be deceived by inclinations merely because of carelessness, instead of summoning it against the malice (of the human heart) which secretly undermines the disposition with soul-corrupting principles.

Considered in themselves natural inclinations are good, i.e. not reprehensible, and to want to extirpate them would not only be futile but harmful and blameworthy as well; we must rather only curb them, so that they will not wear each other out but will instead be harmonized into a whole called happiness. Now the reason that accomplishes this is called prudence. Only what is unlawful is evil in itself, absolutely reprehensible, and must be eradicated. And the reason which teaches this, all the more so when it also puts it in actual practice, alone deserves the name of wisdom, in comparison to which vice may indeed also be called folly, but only when reason feels enough strength within itself to despise it (and every stimulation to it), not just to hate it as something to be feared, and arm itself against it.

However exalted the application of our concepts, and however far up from sensibility we may abstract them, still they will always be appended to image representations, whose proper function is to make these concepts, which are not otherwise derived from experience, serviceable for experiential use. For how would we procure sense and significance for our concepts if we did not underpin them with some intuition (which ultimately must always be an example from some possible experience)? If from this concrete act of the understanding we leave out the association of the image – in the first place an accidental perception through the senses – then what is left over is the pure concept of understanding, whose range is now enlarged and contains a rule for thinking in general. It is in just such a way that general logic comes about; and many heuristic methods of thinking perhaps lie hidden in the experiential use of our understanding and reason; if we understood how to extract these methods carefully from that experience, they could well enrich philosophy with many useful maxims even in abstract thinking.

Of this kind is the principle to which the late Mendelssohn expressly subscribed for the first time, so far as I know, in his last writings (the Morning Hours, pp. 164–165, and the Letters to Lessing's Friends, pp. 33 and 67): namely, the maxim that it is necessary in the speculative use of reason (which Mendelssohn otherwise trusted very much in respect of the cognition of supersensible objects, even so far as claiming for it the evidence of demonstration) to orient oneself by means of a certain guideline which he sometimes called common sense or healthy reason (in the Morning Hours), and sometimes plain understanding (To Lessing's Friends). Who would have thought that this admission would not only have a destructive effect on his favorable opinion of the power of speculative reason when used in theological matters (which was in fact unavoidable), but that even common healthy reason, given the ambiguous position in which he left the employment of this faculty in contrast to speculation, would also fall into the danger of serving as a principle of enthusiasm in the dethroning of reason?

Except for misprints and certain few expressions that have been corrected, nothing has been altered in this edition. Newly added supplements have been placed at the foot of the text, marked with a dagger (†).

Regarding the title of this work (since doubts have been expressed also regarding the intention hidden behind it) I note: Since, after all, revelation can at least comprise also the pure religion of reason, whereas, conversely, the latter cannot do the same for what is historical in revelation, I shall be able to consider the first as a wider sphere of faith that includes the other, a narrower one, within itself (not as two circles external to one another but as concentric circles); the philosopher, as purely a teacher of reason (from mere principles a priori), must keep within the inner circle and, thereby, also abstract from all experience. From this standpoint I can also make this second experiment, namely, to start from some alleged revelation or other and, abstracting from the pure religion of reason (so far as it constitutes a system on its own), to hold fragments of this revelation, as a historical system, up to moral concepts, and see whether it does not lead back to the same pure rational system of religion [from which I have abstracted]. The latter, though not from the theoretical point of view (under which must also be reckoned the technicopractical point of view of pedagogical method, as a technology) may yet, from the morally practical point of view, be independent and sufficient to genuine religion, which, as a rational concept a priori (remaining after everything empirical has been removed), only obtains in this relation. If this is the case, then we shall be able to say that between reason and Scripture there is, not only compatibility but also unity, so that whoever follows the one (under the guidance of moral concepts) will not fail to come across the other as well.

So far as morality is based on the conception of the human being as one who is free but who also, just because of that, binds himself through his reason to unconditional laws, it is in need neither of the idea of another being above him in order for him to recognize his duty, nor of an incentive other than the law itself in order for him to observe it. At least it is his own fault if such a need is found in him; but in this case too the need could not be relieved through anything else: for whatever does not originate from himself and his own freedom provides nothing to make up for a lack in his morality. – Hence on its own behalf morality in no way needs religion (whether objectively, as regards willing, or subjectively, as regards capability) but is rather self-sufficient by virtue of pure practical reason. – For, since its laws bind through the mere form of universal lawfulness of the maxims to be adopted in accordance with this lawfulness as the highest condition (itself unconditional) of all ends, morality needs absolutely no material determining ground of the free power of choice, that is no end, either in order to recognize what duty is or to impel its performance; on the contrary, when duty is the issue, morality can perfectly well abstract from ends altogether, and ought so to do. For example, to know whether I should (or even can) be truthful in my testimony before a court of justice, or faithful when someone else's goods entrusted to me are being reclaimed, there is no need to demand an end which I might perhaps propose to myself to realize by my declaration, for what sort of end this would be does not matter at all; rather, one who still finds it necessary to look around for some end when his testimony is rightfully demanded of him, is in this respect already contemptible.

But although on its own behalf morality does not need the representation of an end which would have to precede the determination of the will, it may well be that it has a necessary reference to such an end, not as the ground of its maxims but as a necessary consequence accepted in conformity to them.