A move that reason mandates an actor make.
“We can look back and see that our case of necessity, having an autonomous metabolism, can be recast as simply the only acceptable solution to the most general design problem of life. If you wanna live, you gotta eat. In chess, when there is only one way of staving off disaster, it is called a forced move. Such a move is not forced by the rules of chess, and certainly not by the laws of physics (you can always kick the table over and run away), but by what Hume might call a ‘dictate of reason’. It is simply dead obvious that there is one and only one solution, as anybody with an ounce of wit can plainly see. Any alternatives are immediately suicidal.” (128, Darwin’s Dangerous Idea)
Darwin’s Dangerous Idea by Daniel Dennett