Algebraic theories are a categorical way of describing sets with
extra algebraic structure. A generalization to a higher dimension
leads to algebraic 2-theories which describe categories with extra 
structure. Within this higher dimensional universal algebra there
is the flexibility to replace one algebraic structure with another
(coherence theory). This flexibility is reflected by the fact that 
one can place a Quillen model category structure on the category 
of 2-theories. We shall explore the implied homotopy theory to 
better understand this universal algebra.