Pure (rein) has here a very definite meaning. It is the absolutely a priori. Negatively it signifies that which is independent of experience. Positively it signifies that which originates from reason itself, and which is characterised by universality and necessity.[67] By “pure reason” Kant therefore means reason in so far as it supplies out of itself, independently of experience, a priori elements that as such are characterised by universality and necessity.
Reason (Vernunft) is used in the Critique in three different meanings. In the above title it is employed in its widest sense, as the source of all a priori elements. It includes what is a priori in sensibility as well as in understanding (Verstand). In its narrowest sense it is distinct even from understanding, and signifies that faculty which renders the mind dissatisfied with its ordinary and scientific knowledge, and which leads it to demand a completeness and unconditionedness which can never be found in the empirical sphere. Understanding conditions science; reason generates metaphysic. Understanding has categories; reason has its Ideas. Thirdly, Kant frequently employs understanding and reason as synonymous terms, dividing the mind only into the two faculties, sensibility and spontaneity. Thus in A 1-2, understanding and reason are used promiscuously, and in place of reine Vernunft we find reiner Verstand. As already stated, the term reason, as employed in Kant’s title, ought properly to be taken in its widest sense. Sensibility falls within reason in virtue of the a priori forms which it contains. Kant does not himself, however, always interpret the title in this strict sense. The triple use of the term is an excellent example of the looseness and carelessness with which he employs even the most important and fundamental of his technical terms. Only the context can reveal the particular meaning to be assigned in each case.
The phrase “of pure reason” (der reinen Vernunft) has, as Vaihinger points out,[68] a threefold ambiguity. (1) Sometimes it is a genitive objective. The critical enquiry is directed upon pure reason as its object. This corresponds to the view of the Critique as merely a treatise on method. (2) Sometimes it is a genitive subjective. The critical enquiry is undertaken by and executed through pure reason. This expresses the view of the Critique as itself a system of pure rational knowledge. (3) At other times it has a reflexive meaning. Pure reason is subject and object at once. It is both subject-matter and method or instrument. Through the Critique it attains to self-knowledge. The Critique is the critical examination of pure reason by itself. The first view would seem to be the original and primary meaning of the title. The second view very early took its place alongside it, and appears in many passages. The third view must be taken as representing Kant’s final interpretation of the title; it is on the whole the most adequate to the actual content and scope of the Critique. For the Critique is not merely a treatise on method; it is also a system of pure rational knowledge. It professes to establish, in an exhaustive and final manner, the a priori principles which determine the possibility, conditions, and limits of pure rational knowledge.[69]
MOTTO
DE nobis ipsis silemus: De re autem, quae agitur, petimus: ut homines eam non opinionem, sed opus esse cogitent; ac pro certo habeant, non sectae nos alicuius, aut placiti, sed utilitatis et amplitudinis humanae fundamenta moliri. Deinde ut suis commodis aequi ... in commune consulant ... et ipsi in partem veniant. Praeterea ut bene sperent, neque instaurationem nostram ut quiddam infinitum et ultra mortale fingant, et animo concipiant; quum revera sit infiniti erroris finis et terminus legitimus.
This motto, which was added in the second edition, is taken from the preface to Bacon’s Instauratio Magna, of which the Novum Organum is the second part. As the first part of the Instauratio is represented only by the later, separately published, De Augmentis Scientiarum, this preface originally appeared, and is still usually given, as introductory to the Novum Organum.
The complete passage (in which I have indicated Kant’s omissions) is rendered as follows in the translation of Ellis and Spedding:[70]
“Of myself I say nothing; but in behalf of the business which is in hand I entreat men to believe that it is not an opinion to be held, but a work to be done; and to be well assured that I am labouring to lay the foundation, not of any sect or doctrine, but of human utility and power. Next, I ask them to deal fairly by their own interests [and laying aside all emulations and prejudices in favour of this or that opinion], to join in consultation for the common good; and [being now freed and guarded by the securities and helps which I offer from the errors and impediments of the way] to come forward themselves and take part [in that which remains to be done]. Moreover, to be of good hope, nor to imagine that this Instauration of mine is a thing infinite and beyond the power of man, when it is in fact the true end and termination of infinite error.”