“The first and highest of all the spheres is that of the fixed stars, self-containing and all-containing, and consequently immobile, in short the locus of the universe, by relation to which the motion and position of all the other heavenly bodies have to be reckoned.”[139] Now it is this doctrine, and this doctrine alone, to which Kant is referring in the passages before us, namely, Copernicus’ hypothesis of a subjective explanation of apparently objective motions. And further, in thus comparing his Critical procedure to that of Copernicus, he is concerned more with the positive than with the negative consequences of their common hypothesis. For it is chiefly from the point of view of the _constructive_ parts of the _Aesthetic_, _Analytic_, and _Dialectic_ that the comparison is formulated. By means of the Critical hypothesis Kant professes on the one hand to account for our scientific knowledge, and on the other to safeguard our legitimate metaphysical aspirations. The spectator projects his own motion into the heavens; human reason legislates for the domain of natural science. The sphere of the fixed stars is proved to be motionless; things in themselves are freed from the limitations of space and time. “Copernicus dared, in a manner contradictory of the senses but yet true, to seek the observed movements, not in the heavenly bodies, but in the spectator.”[140] In view of Kant’s explicit elimination of all _hypotheses_ from the _Critique_[141] the employment of that term would seem to be illegitimate. He accordingly here states that though in the _Preface_ his Critical theory is formulated as an hypothesis only, in the _Critique_ itself its truth is demonstrated _a priori_. * * * * * =Distinction between knowing and thinking.=[142]--Since according to Critical teaching the limits of sense-experience are the limits of knowledge, the term knowledge has for Kant a very limited denotation, and leaves open a proportionately wide field for what he entitles thought. Though things in themselves are unknowable, their existence may still be recognised in thought. INTRODUCTION I shall first[143] give a restatement, partly historical and partly explanatory, of Kant’s main argument as contained in the enlarged _Introduction_ of the second edition.