BUFFO N AND THE PROBLEM OF SPECIES 467 



to link them together by the force of analogy, and to endeavor to attain that 

 high degree of knowledge in which particular effects are recognized as de- 

 pendent upon more general effects, nature is compared with herself in her 

 larger processes, and thus ways are opened before us by which the different 

 parts of physical science may be perfected. For success in the former sort of 

 study there are needful only a good memory, assiduity and careful attention; 

 but for the sort of which we are here speaking other qualities are requisite: 

 breadth of view, steadiness of vision, a power of reasoning formed by the 

 practise of reflection even more than by learning. For such study, in short, a 

 man must have that quality of mind which enables him grasp remote relations 

 between things, to bring them together, and thereby to form a body of reasoned 

 conclusions, after having duly estimated similarities and weighed probabilities. 



But these judicious and stimulating, if slightly vague, appeals for 

 the conversion of natural history into a science of causal relations and 

 generalized laws, were not the principal purpose of the preliminary dis- 

 course. The thought of Buffon at the time when he wrote that essay 

 seems to have been dominated above all by a single idea, which was also 

 one of the two or three ruling ideas of the whole of the first half of the 

 eighteenth century — namely, the Leibnitian "principle of continuity'* 

 (lex continui). In the intellectual fashions of this period, next to the 

 blessed word " Nature " the most sacred phrase was " the Great Chain 

 of Beings " ; indeed, one of the truths that man was supposed to know 

 most surely about nature was that she " makes no leaps." In the form, 

 especially, of the neo-Platonic and Spinozistic metaphysical assumption 

 that all possible forms must exist, the principle was much older than the 

 philosophy of Leibniz; 7 but it owed to him and his disciples a more 

 definite formulation and a greatly increased popular currency. It de- 

 clared that all entities are arranged in a graded scale of similarity, so 

 that for every being that exists there also exists some other (in the strict 

 version of the principle, one and only one other) from which its differ- 

 ence is infinitesimal, i. e., less than any assignable difference. A typical 

 statement of the doctrine is Bonnet's : 8 



Between the lowest and the highest degree of corporeal or spiritual per- 

 fection there is an almost infinite number of intermediate degrees. The series 

 of these degrees constitutes the Universal Chain. It unites all beings, binds 

 together all worlds, embraces all spheres. One Being alone is outside of this 

 chain, and that is He who made it. . . . There are no breaks (sauts) in nature; 

 all is graduated, everything shades off into the next thing. If, between any 

 two beings whatever, there existed a gap, what would be the reason of the 

 transition from the one to the other? There is, therefore, no being above or 

 below which there is not some other that approximates it with respect to some 

 characters and diverges from it with respect to others. 



All this (as Bonnet's language intimates) was held by the Leibni- 

 tian philosophy to be logically implied by the still more fundamental 

 " principle of sufficient reason." For if the gradations found in nature 



7 This implied that there must be one, and can be only one, sample of every 

 possible kind or degree of entity. To consider Leibniz's attitude toward this 

 form of the principle would involve too much technical metaphysics. 



8 " Contemplation de la Nature" (1764), 2d ed., 1769, I., 26-27. 



