There are three kinds of preemptions
One is when you preempt by attacking an opponent on your own initiative; this is called preemption from a state of supension.
Another is when you preempt by attacking an opponent making an attck on you; this is called preemption from a state of waiting.
Yet another is when you and an opponent attack each other simultaneously; this is called preemption in a state of mutual confrontation.
" The Book of Five Rings " Miyamoto Musashi