In cooking , reduction is the process of thickening a liquid mixture such as a sauce by evaporation. Reduction is a difficult piece of philosophical terminology. So, for example, if we reduce the mental to the physical, then whenever we talk of pains, thoughts, and decisions, we can be understood as talking about physical events in the brain. Not necessarily and usually not. Here is an example of a reduction from metaphysics .
Philosophers mean about the same thing when they talk about what exists ultimately .
For example, the bundle theory says that ultimately , properties and bundles thereof exist, rather than objects.