certainly be allowed; but that only means that we might meet with them in the possible progress of experience; for everything is real that stands in one context with a perception according to laws of empirical progress. They are real, therefore, if they stand in an empirical connection with my actual consciousness, although that does not make them real in themselves, that is, apart from this progress of experience... There is nothing really given us except the perception and the empirical progress from this perception to other possible perceptions. For in themselves phenomena, as mere ideas, are real only in perception, and perception is in fact nothing but the reality of an empirical idea, that is, a phenomenon. To call a phenomenon a real thing before it is perceived means either that in the progress of experience we must meet with such a perception, or it means nothing at all... Phenomena are not anything in themselves but mere ideas, which when they are not given to us (in perception) are not met with anywhere at all."
This elaborate passage might be reinforced by many emphatic expressions on Kant's part to the same effect. Thus he warns us that "all objects without exception with which we busy ourselves are in me, that is, determinations of my identical self." He speaks of the mind as prescribing laws a priori to nature, and of nature as submitting to the legislation of the understanding; but he smooths the paradox for us by reminding us that "this nature is in itself nothing but a sum of phenomena, consequently not a thing-in-itself but only a number of ideas in my mind (eine Menge von Vorstellungen des Gemüths)." In such passages there is no mistaking Kant's meaning; even in his phraseology he recalls Berkeley and Mill, except that for associated sensations we have rationally constructed perceptions. Otherwise Kant's phenomenal world of present perceptions and possible perceptions corresponds exactly to Mill's world of actual sensations and permanent possibilities of sensation or Berkeley's world of actual and possible sense-phenomena. The recurring phrase of the Critique, "possible experience," is itself significant of the affinity of standpoint. It may be observed also that when this view is firmly held, as in
