constituent part of it; yet it cannot be given in any experience, but is only _thought_, and thought indeed as that which is absolutely inert, inactive, formless, and without qualities, and which is yet the supporter of all forms, qualities, and effects. Accordingly, of all fleeting phenomena, thus of all manifestations of natural forces and all living beings, matter is the _permanent substratum_ which is necessarily produced by the forms of our intellect in which the world as _idea_ exhibits itself. As such, and as having sprung from the forms of the intellect, it is entirely _indifferent_ to those phenomena themselves, _i.e._, it is just as ready to be the supporter of this force of nature as of that, whenever, under the guidance of causality, the necessary conditions appear; while it itself, just because its existence is really only _formal_, _i.e._, is founded in the _intellect_ must be thought as that which under all that change is absolutely permanent, thus with regard to time is without beginning and without end. This is why we cannot give up the thought that anything may be made out of anything, for example, gold out of lead; for this would only require that we should find out and bring about the intermediate states which matter, in itself indifferent, would have to pass through upon that path. For _a priori_ we can never see why the same matter which is now the supporter of the quality lead could not some time become the supporter of the quality gold. Matter, as that which is only _thought_ _a priori_, is distinguished from the _a priori_ _intuitions_ or _perceptions_ proper by the fact that we can also think it entirely away; space and time, on the contrary, never. But this only shows that we can present to ourselves space and time in imagination without matter. For the matter which has once been placed in them, and accordingly thought as _existing_, we can never again absolutely think away, _i.e._, imagine it as vanished and annihilated, but are always forced to think of it merely as transferred to another space. So far, then, matter is as inseparably connected with our faculty of knowledge as space and time themselves. Yet even the difference that it must first be voluntarily thought as existing indicates that it does not belong so entirely and in every regard to the _formal_ part of our knowledge as space and time, but also contains an element which is only given _a posteriori_. It is, in fact, the point of connection of the empirical part of our knowledge with the pure and _a priori_ part, consequently the peculiar foundation‐stone of the world of experience.