QUOTE : There is no logical reason, however, why, in the unfolding of scientific ideas, several theories may not offer alternative but equally valid and important accounts of a particular aspect of nature. Why must some of these theories be rejected almost as a matter of course? It could be objected that if the number of alternative theories became too large, then the whole scientific enterprise would become excessively diffuse and diluted. It is certainly true that without any established limits, ideas do tend to diverge from each other. However, there is also a natural tendency within scientific thinking for ideas to converge as well. Intelligent and creative perception of the different theories may, for example, give rise to new metaphors in which ideas are gathered together and the similarities and differences between them are explored and unfolded.