SPECIES, in logic, a relative term, ex pressing an idea which is comprised un der some general one, called a genus. The idea of a species is formed, by adding a new idea to the retina: thus if the ge nus be a circumscribed space, and we sup pose this circumscription to be by lines, we shall obtain the notion of that species of figures which are called plain figures; but if we conceive the circumscription to be by surfaces, we get an idea of the spe cies of solid figures. This superadded idea is called the specific difference, not only as it serves to distinguish the spe cies from the genus; but because, being different in all the several subdivisions, we thereby also distinguish the species one from another : and as this superadtled conception completes the notion of the species, it is plain that the genus and specific difference are the proper and constituent parts of the species. If we
trace the progress of the mind still fur ther, and observed it advancing through the inferior species, we shall find its man ner of proceeding to be always the same ; since every lower species is formed, by superadding some new idea to the species next above : thus, if animal be the genus, by superadding the notion of four limbs, we obtain the idea of quadrupeds ; if to this we add further, the peculiar form and characters which distinguish man kind, we get the idea of the human spe cies; and by adding the peculiarities which distinguish a particular person from all others, we form the notion of an indi vidual, which is called the last species, or species specialissimum.
For the use of the genus, species, and specific difference in defining things, see DEFINITION.