Entry 0207: Remarks on the Principle of Non-Contradiction (IV)
Human action presupposes the principle of non-contradiction:
People who act do something indicating that they have a goal and think that certain means, which they are undertaking, is the way to reach that goal.
We act because we believe certain things and have certain goals, which is to say that we do not believe the opposite things and have the oppose goals.
In any particular action, we do not act as though things were anything or everything.
Accordingly, action itself presupposes the principle of non-contradiction. 
↑ Trudy Govier, Socrates' Children: Thinking and Knowing in the Western Tradition, Peterborough, Ontario, Canada: Broadview Press, 1997, pp. 68-69.