  We investigate the structure common to causal theories that attempt to
explain a (part of) the world. Causality implies conservation of identity,
itself a far from simple notion. It imposes strong demands on the
universalizing power of the theories concerned. These demands are often met by
the introduction of a metalevel which encompasses the notions of 'system' and
'lawful behaviour'. In classical mechanics, the division between universal and
particular leaves its traces in the separate treatment of cinematics and
dynamics. This analysis is applied to the mechanical theories of Newton and
Leibniz, with some surprising results.
