[42] Prol., § 11.
[43] Prol., § 10.
[44] Kant expresses the assertion that space is the form of all objects by saying that space is the form of phenomena. This of course renders easy an unconscious transition from the thesis that space is the form of objects to the quite different thesis that space is the form of sensibility; cf. p. 39.
[45] Cf. Prol., Section 8.
[46] Prol., § 9 (cf. p. 55).
[47] The difficulty with which Kant is struggling in the Prolegomena, §§ 6-11, can be stated from a rather different point of view by saying that the thought that geometrical judgements imply a perception of empty space led him to apply the term 'a priori' to perception as well as to judgement. The term, a priori, applied to judgements has a valid meaning; it means, not that the judgement is made prior to all experience, but that it is not based upon experience, being originated by the mind in virtue of its own powers of thinking. Applied to perception, however, 'a priori' must mean prior to all experience, and, since the object of perception is essentially individual (cf. B. 741, M. 435), this use of the term gives rise to the impossible task of explaining how a perception can take place prior to the actual experience of an individual in perception (cf. Prol., § 8).
[48] Cf. p. 17.
[49] For the reasons which led Kant to draw this distinction between empirical and a priori judgements, cf. pp. 21-2.
[50] The same criticism can be urged against Kant's appeal to the necessity of constructing geometrical figures. The conclusion drawn from the necessity of construction is stated thus: "If the object (the triangle) were something in itself without relation to you the subject, how could you say that that which lies necessarily in your subjective conditions of constructing a triangle must also necessarily belong to the triangle in itself?" (B. 65, M. 39). Kant's thought is that the laws of the mind's constructing nature must apply to objects, if, and only if, the objects are the mind's own construction. Hence it is open to the above criticism if, in the criticism, 'construct' be substituted for 'perceive'.
[51] Prol., § 7.