**Motive (algebraic Geometry)**

In algebraic geometry, a **motive** (or sometimes **motif**, following French usage) denotes 'some essential part of an algebraic variety'. To date, pure motives have been defined, while conjectural mixed motives have not. Pure motives are triples *(X, p, m)*, where *X* is a smooth projective variety, *p* : *X* ⊢ *X* is an idempotent correspondence, and *m* an integer. A morphism from *(X, p, m)* to *(Y, q, n)* is given by a correspondence of degree *n – m*.

As far as mixed motives, following Alexander Grothendieck, mathematicians are working to find a suitable definition which will then provide a "universal" cohomology theory. In terms of category theory, it was intended to have a definition via splitting idempotents in a category of algebraic correspondences. The way ahead for that definition has been blocked for some decades, by the failure to prove the standard conjectures on algebraic cycles. This prevents the category from having 'enough' morphisms, as can currently be shown. While the category of motives was supposed to be the **universal Weil cohomology** much discussed in the years 1960-1970, that hope for it remains unfulfilled. On the other hand, by a quite different route, motivic cohomology now has a technically-adequate definition.

Read more about Motive (algebraic Geometry): Introduction, Definition of Pure Motives, Mixed Motives, Explanation For Non-specialists, The Search For A Universal Cohomology, Conjectures Related To Motives, Tannakian Formalism and Motivic Galois Group

### Famous quotes containing the word motive:

“The *motive* of science was the extension of man, on all sides, into Nature, till his hands should touch the stars, his eyes see through the earth, his ears understand the language of beast and bird, and the sense of the wind; and, through his sympathy, heaven and earth should talk with him. But that is not our science.”

—Ralph Waldo Emerson (1803–1882)