Explain the concept of supervenience

Supervenience is the relationship between two different kinds of facts (or properties) such that A type supervenes on B type if and only if there cannot be a change in A without a change in B. To illustrate this, it is often claimed that aesthetic properties supervene on physical properties - say we have two physically identical Mona Lisas, they have the same distributions of paint on their canvases, same size and so on. This would mean that in order for the first Mona Lisa to be more beautiful than the second there would have to be a change its physical properties (the strokes of paint may need to be more fine for example). In other words, there cannot be a change in the aesthetic properties of the Mona Lisa without a change in the physical properties. In Philosophy of Mind, the concept of supervenience is invoked to support non-reductive Physicalism - the belief that mental states depend solely on physical states, but that mental states cannot be reduced to (are not identical to) physical states. On this view, there cannot be a change in mental states without a change in brain states - so mental states depend on, but are not identical to, physical states.