Reductionism is the belief that any complex set of phenomena can be defined or explained in terms of a relatively few simple or primitive ones. To a reductionist, once a set of equations or mathematical relations has been found to describe a system, then the behavior of the system is considered to be explained. Reductionism is very similar to, and has its roots from, Occam's Razor , which states that between competing ideas, the simplest theory that fits the facts of a problem is the one that should be selected. Reductionism was widely accepted due to its power in prediction and formulation. The 20th century reaction against reductionism is relativism .
Modern science is somewhere in between.
Another way of stating this is that for everything that happens there are conditions such that, given them, nothing else could happen. Implicit to determinism is the fact that every event happens of necessity. Determinism also implies that everything is predictable given enough information. Since Newtonian or classical physics is rigidly determinist, both in the predictions of its equations and its foundations, then there is no room for chance, surprise and creativity. Everything is as it has to be, which gave rise to the concept of a clockwork Universe .