Constraint

A constraint is a limitation of possibilities. In particular, a constraint is a restriction of the feasible solutions in an optimization problem.

In the theory of constraints, it is any factor that limits the performance of a system with respect to its goal.

To take a simple example: a chain has 5 links, each link capable of holding a maximum weight of 5, 7, 4, 8 and 6 tonnes respectively. The maximum weight the chain can hold is clearly 4 tonnes – the limit imposed by the weakest link. In this case, all 5 links have limits to their strength, but the 3rd link is the constraint because it is the greatest restriction on the system.

Eliyahu M. Goldratt maintains that any business system has

• at least one constraint, otherwise its performance would be infinite
• very few constraints, otherwise it would be unstable and cease to exist

The concept of constraint is the basis for Goldratt's process of focused improvement.

See also restraint, Donella Meadows' twelve leverage points to intervene in a system

For constraints in literature, see constrained writing and in theatre, see Theatrical constraints.