this comet-meaning is itself not isolated; it is a related portion of the whole system of astronomic knowledge. Suns, planets, satellites, nebulæ, comets, meteors, star dust--all these conceptions have a certain mutuality of reference and interaction, and when the speck of light is identified as meaning a comet, it is at once adopted as a full member in this vast kingdom of beliefs. [Sidenote: Importance of system to knowledge] Darwin, in an autobiographical sketch, says that when a youth he told the geologist, Sidgwick, of finding a tropical shell in a certain gravel pit. Thereupon Sidgwick said it must have been thrown there by some person, adding: "But if it were really embedded there, it would be the greatest misfortune to geology, because it would overthrow all that we know about the superficial deposits of the Midland Counties"--since they were glacial. And then Darwin adds: "I was then utterly astonished at Sidgwick not being delighted at so wonderful a fact as a tropical shell being found near the surface in the middle of England. Nothing before had made me thoroughly realize _that science consists in grouping facts so that general laws or conclusions may be drawn from them_." This instance (which might, of course, be duplicated from any branch of science) indicates how scientific notions make explicit the systematizing tendency involved in all use of concepts. § 4. _What Conceptions are Not_ The idea that a conception is a meaning that supplies a standard rule for the identification and placing of particulars may be contrasted with some current misapprehensions of its nature. [Sidenote: A concept is not a bare residue] 1. Conceptions are not derived from a multitude of different definite objects by leaving out the qualities in which they differ and retaining those in which they agree. The origin of concepts is sometimes described to be as if a child began with a lot of different particular things, say particular dogs; his own Fido, his neighbor's Carlo, his cousin's Tray. Having all these different objects before him, he analyzes them into a lot of different qualities, say (_a_) color, (_b_) size, (_c_) shape, (_d_) number of legs, (_e_) quantity and quality of hair, (_f_) digestive organs, and so on; and then strikes out all the unlike qualities (such as color, size, shape, hair), retaining traits such as quadruped and domesticated, which they all have in general. [Sidenote: but an active attitude]