The privilege of constructing names where they are wanted, belongs to natural historians no less than to {269} the cultivators of physical science; yet in the ancient world, writers of the former class appear rarely to have exercised this privilege, even when they felt the imperfections of the current language. Thus Aristotle repeatedly mentions classes of animals which have no name, as co-ordinate with classes that have names; but he hardly ventures to propose names which may supply these defects[3\4]. The vast importance of nomenclature in natural history was not recognized till the modern period. [Note 3\4: In his _History of Animals_, (b. i. c. vi.), he says, that the great classes of animals are Quadrupeds, Birds, Fishes, Whales (_Cetaceans_), Oysters (_Testaceans_), animals like crabs which have no general name (_Crustaceans_), soft animals (_Mollusks_ and _Insects_). He does, however, call the Crustaces by a name (_Malacostraca_, soft-shelled) which has since been adopted by Naturalists.] We have, however, hitherto considered only the formation or appropriation of single terms in science; except so far as several terms may in some instances be connected by reference to a common theory. But when the value of technical terms began to be fully appreciated, philosophers proceeded to introduce them into their sciences more copiously and in a more systematic manner. In this way, the modern history of technical language has some features of a different aspect from the ancient; and must give rise to a separate Aphorism. APHORISM II. _In the Modern Period of Science, besides the three processes anciently employed in the formation of technical terms, there have been introduced Systematic Nomenclature, Systematic Terminology, and the Systematic Modification of Terms to express theoretical relations_[4\4]. [Note 4\4: On the subject of Terminology and Nomenclature, see also Aphorisms LXXXVIII and XCVIII concerning Ideas, and b. viii. c. ii. of the _History of Scientific Ideas_. In those places I have spoken of the distinction of _Terminology_ and _Nomenclature_.]