Avicenna's Theory of Mental Existence

So far, we've been thinking about what Avicenna calls external or concrete existence. But he also has the notion of mental existence. In this sense, my sister on the flying trapeze does exist. By contrast, something that really didn't exist at all would be something that never existed in any mind,. Perhaps because the mere thought of it would be absurd. If it really never exists, not even in the mind, then it must be inconceivable and tense impossible.