  There are arguably three versions of the principle of non-contradiction to be found in Aristotle: an ontological, a doxastic and a semantic version. The first version concerns things that exist in the world, the second is about what we can believe, and the third relates to assertion and truth. The first version (hereafter, simply PNC) is usually taken to be the main version of the principle and it runs as follows: “It is impossible for the same thing to belong and not to belong at the same time to the same thing and in the same respect” (with the appropriate qualifications) (Metaph IV 3 1005b19–20). The following are some of those qualifications: The “same thing” that belongs must be one and the same thing and it must be the actual thing and not merely its linguistic expression. For example, it is possible for someone to be a pitcher and not a pitcher where “pitcher” in the first instance refers to a baseball player and in the second to a jug that can hold beer. Also, while it is possible for x to be actually F and potentially not F, it is impossible for something to be actually F and actually not F. A table can be actually red and potentially not red, but not actually red and actually not red at the same time.