2. _Forms of thinking data._--As sensory datum is material set for the work of thought, so the ideational forms with which thought does its work are apt and prompt to meet the needs of the material. The "accessory"[25] notion of ground of coherence turns out, in truth, not to be a formal, or external, addition to the data, but a requalification of them. Thought is accessory as accomplice, not as addendum. "Thought" is to eliminate mere coincidence, and to assert grounded coherence. Lotze makes it absolutely clear that he does not at bottom conceive of "thought" as an activity "in itself" imposing a form of coherence; but that the organizing work of "thought" is only the progressive realization of an inherent unity, or system, in the material experience. The specific modes in which thought brings its "accessory" power to bear--names, conception, judgment, and inference--are successive stages in the adequate organization of the matter which comes to us first as datum; they are successive stages of the effort to overcome the original defects of the datum. Conception starts from the given universal (the common element) of sense. Yet (and this is the significant point) it does not simply abstract this common element, and consciously generalize it as over against its own differences. Such a "universal" is _not_ coherence, just because it does not _include_ and dominate the temporal and local heterogeneity. The _true_ concept (see Vol. I, p. 38) is a system of attributes, held together on the basis of some ground, or determining, dominating principle--a ground which so controls all its own instances as to make them into an inwardly connected whole, and so specifies its own limits as to be exclusive of all else. If we abstract color as the common element of various colors, the result is not a scientific idea or concept. Discovery of a process of light-waves whose various rates constitute the various colors of the spectrum gives the concept. And when we get such a concept, the former mere temporal abruptness of color experiences gives way to organic parts of a color system. The logical product--the concept, in other words--is not a formal seal or stamp; it is a thoroughgoing transformation of data in a given sense.