CLASSIFICATION. 501 



their properties but was not specially interested in any. Classes formed 

 on this principle may be called, in a more emphatic maimer than any oth- 

 ers, natural groups. 



§ 3. On the subject of these groups Di*. Whewell lays down a theory, 

 grounded on an important truth, which he has, in some respects, expressed 

 and illustrated very felicitously, but also, as it appears to me, with some 

 admixture of error. It will be advantageous, for both these reasons, to 

 extract the statement of his doctrine in the very words he has used. 



" Natural groups," according to this theory,* are " given by Type, not 

 by Definition." And this consideration accounts for that " indefiniteness 

 and indecision which we frequently find in the descriptions of such groups, 

 and which must appear so strange and inconsistent to any one who does 

 not suppose these descriptions to assume any deeper ground of connection 

 than an arbitrary choice of the botanist. Thus in the family of the rose- 

 tree, we ai'e told that the ovules are very rarely erect, the stigmata usually 

 sinaple. Of what use, it might be asked, can such loose accounts be ? To 

 which the answer is, that they are not inserted in order to distinguish the 

 species, but in order to describe the family, and the total relations of the 

 ovules and the stigmata of the family are better known by this general 

 statement. A similar observation may be made with regard to the Anoma- 

 lies of each group, Avhich occur so commonly, that Dr. Lindley, in his In- 

 troduction to the Natural System of Botany, makes the 'Anomalies ' an 

 article in each family. Thus, part of the character of the Rosaceae is, that 

 they have alternate stipulate leaves, and that the albumen is obliterated; 

 but yet in Lowea, one of the genera of this family, the stipulae are absent; 

 and the albumen is present in another, Neillia. This implies, as we have 

 already seen, that the artificial character (or diagnosis, as Mr. Lindley calls 

 it) is imperfect. It is, though very nearly, yet not exactly, commensurate 

 with the natural group ; and hence in certain cases this character is made 

 to yield to the general weight of natural affinities. 



"These views — of classes determined by characters which can not be 

 expressed in words — of propositions which state, not what happens in all 

 cases, but only usually — of particulars which are included in a class, though 

 they transgress the definition of it, may probably surprise the reader. 

 They are so contrary to many of the received opinions respecting the use 

 of definitions, and the nature of scientific propositions, that they will prob- 

 ably appear to many persons highly illogical and unphilosophical. But a 

 disposition to such a judgment arises in a great measure from this, that 

 the mathematical and mathematico - physical sciences have, in a great de- 

 gree, determined men's views of the general nature and form of scientific 

 truth ; while Natural History has not yet had time or opportunity to exert 

 its due influence upon the current habits of philosophizing. The appar- 

 ent indefiniteness and inconsistency of the classifications and definitions of 

 Natural History belongs, in a far higher degree, to all other except mathe- 

 matical speculations ; and the modes in which approximations to exact dis- 

 tinctions and general truths have been made in Natural History, may be 

 worthy our attention, even for the light they throw upon the best modes 

 of pursuing truth of all kinds. 



" Though in a Natural group of objects a definition can no longer be of 

 any use as a regulative principle, classes are not therefore left quite loose, 



* History of Scientific Ideas, ii., 120-122. 



