 flames, though there are good reasons for concluding that he made mistakes in them.
It is an old prejudice in philosophy that all statements must be either "empirical statements" or else be “known a priori", that is, independent of experience. This dichotomy goes back to Hume, and was further fixed in the minds of philosophers by Kant. But it is totally false and misleading, like so many other hard and fast antitheses. Thus mathematical principles are not established empirically like the generalisations of the empirical sciences, but they are certainly derived from experience and not known independently of experience. And this is true also of the principles concerning "categories" which are of primary interest to philosophy.
The systematic or methodical investigation of categories has to do with the word‑function of abstraction. Formal logic deals with abstraction only in the way of calculating the logical operations involved in abstracting a conclusion from premises. For instance, from information "All A's that are B are C”, plus information that "This A is C”, can be abstracted the conclusion "This A is C”. This is the sort of abstraction a computer can be programmed to perform. And of course, when very complicated information is fed into it, it can abstract conclusions, as required, which human brains would make very heavy work of abstracting.
But there are procedures of abstraction depending not on the logical form but on the meaning. For instance, from information "This rose is red" may be abstracted "This rose is not white"; and that abstraction does not depend on the logical form of propositions but on meaning. Suppose a rose grower had a computer to tell him how many roses of different colours he had sold, so that for each sale it registered the colour of the rose. It would not work unless in programming it he had been guided by the principle: "These are the colours of roses . . . and a rose of one colour is not of any other colour". But that is not a proposition of formal logic, and is not demonstrable or certifiable by procedures of formal logic. Suitably generalised (for it applies not only to roses), it may be called, after Ryle, a "category proposition".
Propositions stating colour may be termed a category of propositions, distinct from, for example, those stating shape or weight. And obviously, there are principles or rules for abstraction ("category propositions") dealing not only with abstracting one proposition of a given category from another of that category (such as deriving "This is not white" from "This is red"), but also for abstracting propositions of other categories (such as deriving "This has a shape" from "This has a colour"). To go against category rules, or "category propositions", always results in absurdity or non‑informativenesssuch as saying that "So and so's red roses are white", or "So and so's roses have no shape or size".
Such examples or the conclusions of an investigation of categories may well be regarded as trivial and obvious, so that such an investigation may be thought trivial and unnecessary. However, two points are already worth noting.
The first is that a computer has to deal with definite categories of information, and has to be instructed and programmed according to the rules for those categories. The people who build and instruct computers must know those rules before they can make machines that obey them. Computers themselves could not conclude to such rules by any process of their own mechanisms.This is an illustration of the fact that human thought, on the one hand, and what computers do and can conceivably be made to do, on the other, are by no means the same. A machine can quite well be made to observe and record observations and generalise and abstract from what it observes. But just as it does not fall in love with other machines and produce little ones, or co‑operate with other machines in socially producing and distributing their means of sustenance, so it lacks the capacity of developing for itself the categories of thought and the rules for operating with the