QUALITATIVE PLURALISM In the first place the term "pluralism" may have a qualitative meaning. One of the oldest problems of philosophy is that which concerns itself with the question whether the ultimate funda mental stuff, which is the ground of reality, is a single substance or includes a number of substances with differing attributes. Theories founded on the supposition that there are many ulti mate substances, or at any rate more than one, are "pluralistic" in the qualitative sense of the term.
As a matter of fact only one theory of this type has ever been seriously propounded and effectively defended. This is the theory of "dualism," which holds that there are two kinds of fundamental substance. The two substances of dualism are commonly termed "mind" and "matter," and the distinctive attributes assigned to them are not merely different but are strictly incomparable with one another. The essential property of "mind" is thought; that of "matter" is extension. Dualism, which probably approximates more nearly than any other metaphysic to the practical, if un formulated, belief of the ordinary man who does not concern himself with philosophical analysis, recurs at intervals, in one form or another, throughout the history of speculative thought. But the clearest statement and the most able defence of it are to be found in the writings of Descartes (1596-165o), with whom modern philosophy is generally regarded as beginning. Descartes starts from the existence of the self. The fact of consciousness is, he holds, quite undeniable. He then proceeds to deduce the existence of God from the presence in our minds of an idea of God which embraces attributes so exalted as to make it incon ceivable that the idea could have originated in anything so limited as the human mind. Accordingly its presence can only, he thinks, be explained by an external cause, namely, God him self. From this it is an easy step to the existence of matter. For God, being perfect, would not falsify our clearest perceptions; and among these is the perception of matter. Moreover, the attribute of matter which is most distinctly apparent to us is its extension, or occupancy of space, and this must accordingly be regarded as the essentially distinctive property of material substance.
We need not stop to consider in detail the defects of this argu ment which Descartes elaborated with remarkable thoroughness and ingenuity. It is sufficient to point out that the essential
feature of his analysis, namely, the division of reality into mind and matter, was at fault. Matter as he conceived it, so far from being a substance and therefore concrete in the most complete sense, was altogether abstract. The same is true, though to a lesser extent, of his conception of mind. In fact the dualistic division of the universe into mind and matter, though it starts, as all philosophical theories must start, from the elements given in immediate experience, proceeds by abstracting some of these ele ments and elevating them to the position of concrete entities in their own right. This process, useful and indeed necessary for the purposes of such bodies of knowledge as the special sciences, is too artificial to yield anything of metaphysical value. Meta physics, to achieve its end, must keep in constant touch with the concrete, that is, with experience. But a process of reasoning like that adopted by Descartes inevitably tends further and further away from the concrete to the abstract. The practical consequences of this for dualism are seen in its inability to attack with any success such problems as those concerned with the relation of body and mind, the nature of the external world, and the question as to how knowledge is possible at all.
Dualism is the only form of qualitative pluralism which has ever been seriously developed. (But it should perhaps be pointed out that the cosmology of Empedocles [490-430 B.c], with its four elements, earth, air, fire, water, together with the qualitative atomism of his follower Anaxagoras, who regarded the universe as made up of a countless number of qualitatively simple ele ments, are really forms of qualitative pluralism.) It is true that some of the doctrines of theosophy and allied systems appear to tend to a pluralism of more than two kinds of substance, but these doctrines are essentially speculative and have never been de veloped in a form sufficiently definite, nor defended by argu ments sufficiently logical, to affect at all seriously the develop ment of philosophical thought. We may therefore conclude this brief survey of qualitative pluralism and pass on to consider quantitative pluralism.