...In spite of the ciarity of the definitions involved  in the theory of the ontological square, the associated terminology has often tended to be dangerously ambiguous (for example 'inesse' as a term designating ieither one of the two basic relations; 'accident' as referrïng both to universal and to Individual accidents)

Two powerful ideas have acted against 'the sharp separation of the four classes of entities:

1. the notîon of essence.

2. the view of universals as merely 'mental',

so that the only real classification bas been held by many to be the division hetween accidents and substances...

Quantity: