Thē'o-ry, n.

[Fr. théorie, It. & Sp. teoria, Lat. theoria, Gr. θεωρία, from θεωρεῖν, to look at.]

1Sense 1. A doctrine, or scheme of things, which terminates in speculation or contemplation, without a view to practice; hypothesis; speculation.

☞ “This word is employed by English writers in a very loose and improper sense. It is with them usually convertible into hypothesis, and hypothesis is commonly used as another term for conjecture. The terms theory and theoretical are properly used in opposition to the terms practice and practical. In this sense, they were exclusively employed by the ancients; and in this sense, they are almost exclusively employed by the continental philosophers.” Sir W. Hamilton.

2Sense 2. An exposition of the general principles of any science; as, the theory of music.

3Sense 3. The science distinguished from the art; as, the theory and practice of medicine.

4Sense 4. The philosophical explanation of phenomena, either physical or moral; as, Lavoisier’s theory of combustion; Smith’s theory of moral sentiments.

Synonyms— Hypothesis; speculation. — THEORY, HYPOTHESIS. The following statement of the difference between a theory and an hypothesis, is derived from the writings of De Quincey. With some slight variation, it is given in his own words. “A theory may be thus described: Imagine, in any science or speculation, that all the elements (that is, the forces, the modes of action, the phenomena, &c.) are given; but as yet they exist to the mind as an unorganized chaos. Then steps in contemplation, or reflective survey (θεωρία), to assign to them all their several places or relations: which shall be first, which middle, which last; which shall be end, which shall be means; which subordinate, which co-ordinate; which force is for impulse, which for regulation; which absolute, which conditional; which purpose direct, which indirect or collateral; and so on. This introduction of organization among the facts or data of science is theory. A theory, therefore, may be defined an organic development to the understanding of the relations between the parts of any systematic whole. In an hypothesis, on the other hand, it is only one relation which is investigated; viz., that of dependency. A number of phenomena are given, and perhaps with no want of orderly relation among them; but as yet they exist without apparent basis or support. The question, therefore, is concerning a sufficient ground or cause to account for them. I therefore step in, and underlay the phenomena with a substructure, or sub-position (ὑπόθεσις), such as I think capable of supporting them. This is an hypothesis. Briefly, then, in a theory, I organize what is certain enough already, but undetermined in its relations; whereas, in an hypothesis, I assign the causality, when previously it was either unknown or uncertain. For example, we talk properly of a theory of combustion; for the elements, that is, the phenomena and results, are indeterminate only with regard to their reciprocal relations. But with regard to the aurora borealis, it is an hypothesis that we want in the first place, for the phenomena are of uncertain origin. And perhaps this hypothesis would demand, as its sequel, a theory of the whole agencies concerned; but this could not be until the causality should have been determined. Again, suppose the case of algebraical equations: here all possibility of hypothesis is excluded. But a theory is still wanted. Many theories have started from the genesis of equations first proposed by Harriot; viz., that which views the higher equations as generated by multiplication out of the lower. But, perhaps, a different view of their origin would lead to more comprehensive results. Hindenburg, with his disciples, Stahl, &c., have most happily applied an approved theory of combinations to this subject.”