"To understand ‘x’, we need to know what it is to be x, or to be an x, and that knowing this apprises us of what it is NOT to be x, not to be an x. But with ‘real’… it is the negative that wears the trousers. That is, a definite sense attaches to the assertion that something is real, a real such-and-such, only in the light of a specific way in which it might be, or might have been, NOT real."
J.L Austin - Sense and Sensibilia. 1962.