When opening a dictionary at the letters P. H. E. we should soon arrive at the word Phenomenon and its meaning: whatever is presented to the senses, or affects us physically or morally.
As long as knowledge comes to us only by the way of our senses, it follows that in speaking of affinity, electricity and magnetism as natural phenomena, which are known to us only by their effect on Space and Time, we speak in accordance with our method of representation, and not as they are in themselves, since we have not the least idea what these natural forces are in themselves. We recognise musical sounds because our ears hear them, and we appreciate colours because our eyes see them; we take cognisance of them as they appear to us, but we are ignorant of both the one and the other as they are in actuality, that is independently of our organs which correspond to them. Thus all the objects that we know—from the manner of our knowledge—become for us phenomena, and the world in which we live is a world of phenomena.
The Categories of the Understanding.
Besides these fundamental forms of sensuous intuition Space and Time, Kant by his analysis of Pure Reason discovered other conditions of our knowledge which could not have come from without. He divides them into twelve distinct classes, and in the phraseology of philosophy they are called Categories of the Understanding. Aristotle had previously arranged a table of Categories, but in his Logic Aristotle concerns himself with the laws of thought in general, the abstraction derived from the practical use made of them; whilst Kant studies the facts first themselves, or first principles, in their relation with certain fixed objects.
The different categories have certain traits in common, not a single one of our thoughts but will find a place in the one or the other. Another feature which characterises all is, that without them no experience would be possible, they rule our understanding. This is very marked in the category called Plurality. Let us try to think of anything without thinking of it at the same time as one or many, and we shall find it an impossibility. We cannot think of an apple or speak of an apple without picturing more than one; and Max Müller has demonstrated that rational speech is impossible, if we cannot when speaking decide whether the subject of a sentence consists of one or many.
Cause and Effect.
The ideas of Cause and Effect belong to those first principles that reason draws from itself, and the category of causality is one of the most important. We never experience a sensation, of whatever kind, without attaching it, involuntarily and necessarily, to some external object which we know possesses the qualities corresponding to our sensations. Thus the impressions of heat or cold, sweet or bitter, blue or yellow, evoke immediately the picture of certain objects which are hot or cold, such as fire or ice; or which are sweet or bitter, such as sugar or absinth; or blue, as the sky; or yellow, as the lemon; and these external objects we consider as the causes, and our bodily sensations as the effects.
Axioms.
There are certain universal truths which are self-evident, and were evolved not by experience only or argument, nor science, as they are the natural appanage of common-sense, e.g., such axioms as the following: the whole is greater than the part; a straight line is the shortest distance between two points; each body occupies space; every event occupies time; every effect has a cause. All these are more certain than that the sun will rise to-morrow; common-sense has always known them, and the entire human race has not waited for the coming of Kant to recognise these facts.
It is strange that the majority of men who know so many things that are true by intuition, often make mistakes when they begin to reflect. They imagine that all things falling under their observation have the power of making themselves known directly, as if they entered an empty space in the imagination which was ready to receive them. Are they ignorant of the fact that in order to think of an external object, it is not necessary to have it in actuality—as it exists in nature—before one’s eyes, but that it suffices to imprint its image on the mind? This is very simple, and no doubt common-sense itself would see a truism which might be passed in silence. “What is there extraordinary,” common-sense might say, “if in thinking of a lemon, for instance, there should be at once presented to the mind a yellow fruit, of acid flavour, and of a certain shape—a lemon in fact?”