Note 181 — Introductory material

I have already indicated, in general terms, the ground for regarding as à priori the properties of any form of externality. This ground is transcendental, i.e. it is to be found in the conditions required for the possibility of experience. The form of externality, like Riemann's manifolds, is a general class-conception, including time as well as Euclidean and non-Euclidean spaces. It is not motived, however, like the manifolds, by a quantitative resemblance to space, but by the fact that it fulfils, if it has more than one dimension, all those functions which, in our actual world, are fulfilled by space. But a form of externality, in order to accomplish this, must be, not a mere conception, but an actually experienced intuition. Hence the conception of such a form is the general conception, containing under it every logically possible intuition which can fulfil the function actually fulfilled by space. And this function is, to render possible experience of diverse but interrelated things. Some form in sense-perception, then, whose conception is included under our form of externality, is à priori necessary to experience of diversity in relation, and without experience of this, we should, as modern logic shows, have no experience at all. This still leaves untouched the relation of the à priori to the subjective: the form of externality is necessary to experience, but is not, on that account, to be declared purely subjective. Of course, necessity for experience can only arise from the nature of the mind which experiences; but it does not follow that the necessary conditions could be fulfilled, unless the objective world had certain properties. The ground of necessity, we may safely say, arises from the mind; but it by no means follows that the truth of what is necessary depends only on the constitution of the mind. Where this is not the case, our conclusion, when a piece of knowledge has been declared à priori, can only be: Owing to the constitution of the mind, experience will be impossible unless the world accepts certain adjectives.