File:320px-Reduktionismus.png

An illustration of multiple realizability. M stands for mental and P stand for physical. It can be seen that more than one P can instantiate one M but not vice versa. Causal relations between states are represented by the arrows (M1 goes to M2, etc.)

Summary
from German wikipedia http://de.wikipedia.org/wiki/Reduktionismus#Multiple_Realisierungen