  The final chapter of the Metaphysical Foundations, the Phenomenology, focuses on how the motion of matter can be experienced modally, that is, in terms of it being possibly, actually, or necessarily in motion. Its three Propositions specify (in accordance, Kant suggests, with the results of the three previous chapters) that (i) rectilinear motion is a merely possible predicate of matter, (ii) circular motion is an actual predicate of matter, and (iii) the equal and opposite motion of one matter with respect to another is a necessary motion of that matter. In the General Remark to the Phenomenology, Kant discusses the status of absolute space, which had been presupposed by the possible, actual, and necessary motions of matter at issue in the three main propositions, and explains that since it is not itself an object of experience, it must be represented by means of an idea of reason (in Kant's technical sense of “idea”, namely as a concept for which a corresponding object could never be given to us in intuition). Though we can never know absolute space, it nonetheless functions as a regulative principle that guides us in our scientific practice by forcing us to look for further conditions for the conditioned objects we meet with in experience. Kant's view that ideas of reason can function as regulative principles is developed in the Appendix to the Transcendental Dialectic in the Critique of Pure Reason.