direct product


Category theory

Limits and colimits

Direct products


In universal algebra, a direct product is simply a product in a concrete category that is created by the forgetful functor.

Compare the direct sum, a more complicated concept.


Trivially, a cartesian product of sets is a direct product in Set.

One of the requirements of a topological category is that any family of objects must have a direct product, although the term ‘direct product’ is not used in topology.

Many algebraic categories, such as Grp, Ab, Ring, etc, also have all direct products; this is where the term ‘direct product’ originated.

The category of (SetSet-valued) models of any Lawvere theory has all direct products; this includes the examples from algebra above.

Revised on August 26, 2012 23:54:41 by Urs Schreiber (