DIALECTICAL CONTRADICTION IN THE SCIENCES 49^ illusion and fantasy."1 Neil Smith $tatea that "...tbe dial^ctic^ cannot be conceived as existing outside human experience of the world. To seek a dialectic in nature, divorced from the human appropriation of nature, is to indulge in metaphysics/^ The t^lst of dialectics, as Engels said, is in nature. The question that we should aisled whether processes in nature ^ characterised by the unity, a8xl struggle of opposHes, whether they pass tfarougb stages of quantitative .growth and qualitative leaps, changes from one quality into its polar opposite, and so on, independent of observation by human beings. All the sciences show th^t the principles of dialectics operate in natwal processes. The principles of dialectics have bew abstracted from the widest range ^of human experience^ It is in this sense that. the laws ©f dialectics have been described as the most general laws of development of nature, society and thought^ Contradiction Of all the laws of dialectics the central one is concerned with the unity and struggle ofopposites and the corresponding category of contradiction. I shall consider in this paper only this central feature of dialectics and show how this particular law is manifested in nature* I shall also try to show how the operation of thi? law in nature has its reflection in our thinking, in the contradictions that arise io our theories at crucial stages in the development of the sciences, and how these contradictions are resolved. The anpient Greek philosophers of the Milesian school had grasped the essence of reality when they stated that change was fundamental in nature. Heraclitu^ said, "'AH things flow, all change. It is impossible to enter twice into one and the same stream.'* It was in a sense natural to proceed to the next step of understanding the motion of things as a unity of opposite features, and indeed tfa^ Eleatic philosophers gfa&ped this essence of motion. But being incorrigible idealists, having expressed motion in terms of contradictions they tried to use (his to disprove motion itself. Movement itself is a contradiction and so movement cannot be real, they declared. Watching a bird in flight across a river the ancient philosopher must have noticed that what was here is changed to there. Here a^d there are opposite terms (exclusive terms). The flight of the bird therefore unites these opposites. This idea was developed by Zena one of the best knpwn of the Eleatics, in the form of four paradoxes, to show that motion was a contradiction. The fapaous paradoxes of the arrow in flight and of Achilles and the .tortoise give the general lin^ ©f argument. The paradox of the ar^ow runsibice tbi^. An arrow in flight has to be sam^vhere, say the arrow A is at tAe point B. But then sin^e it is in flight the arrow cannot be at B. Thus we h^ve the contradiction: The arrow A is at B and the arrow A is not at B We shall see later how this contradiction is resolved, but we shall now