Consider the statement that John is thinking about a unicorn. This could be true even if no unicorn actually exists. But surely John is thinking about something. His mind is not simply a blank. Some philosophers have wanted to say in such a case that there is an object — in fact, a unicorn -- about which John is thinking, but that this object is one that has “intentional inexistence”. It exists merely as an object of thought. In Psychology from an Empirical Standpoint, Brentano said that every psychical phenomenon is characterized by “intentional inexistence”. He went on to say that this intentional inexistence is “exclusively peculiar to psychical phenomena. No physical phenomenon shows anything similar”.