Page "Phase space" Paragraph 4

In classical mechanics, any choice of generalized coordinates q < sup > i </ sup > for the position ( i. e. coordinates on configuration space ) defines conjugate generalized momenta p < sub > i </ sub > which together define co-ordinates on phase space.

More abstractly, in classical mechanics phase space is the cotangent space of configuration space, and in this interpretaton the procedure above expresses that a choice of local coordinates on configuration space induces a choice of natural local Darboux coordinates for the standard symplectic structure on a cotangent space.