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.