of our mind; the difference between them being, that while time is an abstraction of the whole—perceptual and non-perceptual—content of the mind, space is an abstraction from the first only, from the events, from Experience. The definition of this relation is given by its being the only relation, common to all and any two parts of this content. Space and time as such are not subjects of physical experience, they are pure concepts, abstractions from experience; therefore they have no physical properties, properties which it would be possible to examine and determine by physical means. Properties which can be determined and measured by physical means are not properties of space and time, but of that which is “in” space and time (which means, according to our definition, that which is arranged in spatio-temporal order)—i.e., of Experience. It is, therefore, meaningless to speak about the “measurement” of space and time, still less about their metrical properties: what we are doing when we “measure” space (or time) is (assuming for the moment that we know what we mean by the word measurement)—measuring Experience, having regard only to its order in respect of space (or alternatively time), and leaving aside its order of time (or alternatively space).
47.1. At this point it is necessary to remark that order itself is not the only relation which it would be possible to call spatial or temporal, i.e., which would be common to all parts of Experience; the second relation of this kind—as long as we have not analysed Experience into its elements—is extension. Extension is so often considered to be the property defining space and time that it is necessary briefly to justify our choice of order as the space—and time—defining relation. The reasons by which we were led in our choice are roughly these: in the first place, extension is a characteristic of Experience as a whole, but loses all meaning when we think of Experience as analysed into (unextended) elements, and here the relation of order is at a great advantage. Secondly, extension as a pure space and time characteristic appears in the Geometry of Experience when we introduce the relation of interval between two elements, and it can be considered to be only another facet of the same relation of which one facet is order: this being understood, we can finally say that we were led by the same reasoning which compels us to consider analysis situs to be a more fundamental branch of geometry than metric geometry. That, of course, may be a matter of opinion: I do not doubt that it is possible to proceed in the contrary diirecton and arrive at results equally fundamental.
