M ichelle M ontague In asserting that physical phenomena are mere appearances, however, Brentano’s starting point is very different On his terms, ‘physical phenomena’ are not part of any experience-transcending mind-independent reality, but only signs of something that is transcendent in this way A physical phenomenon is an appearance created by our causal relation to something independent of us As such, physical phenomena cannot give us knowledge of how things ‘really and truly are’ He puts this point variously by saying that The phenomena of light, sound, heat, spatial location and locomotion . . are not things which really and truly exist They are signs of something real, which, through its causal activity, produces presentations of them They are not, however, an adequate representation of this reality, and they give us knowledge of it only in a very incomplete sense We can say that there exists something which, under certain conditions, causes this or that sensation We can probably also prove that there must be relations among these realities similar to those manifested by spatial phenomena, shapes and sizes But this is as far as we can go We have no experience of that which truly exists, in and of itself, and that which we experience is not true The truth of physical phenomena is, as they say, only a relative truth (14/19) we have no right . . to believe that the objects of so-called external perception really exist as they appear to us Indeed, they demonstrably not exist outside of us In contrast to that which really and truly exists, they are mere phenomena (7/10) We have nevertheless seen how the expression “physical phenomena” is sometimes erroneously applied to . . forces themselves (76/100) So the subject matter of the natural sciences, according to Brentano, is physical phenomena, e.g color, sound, warmth and odor, all of which are appearances Natural sciences not directly study ‘things in themselves’, even though some people mistakenly think they So much for physical phenomena What about mental phenomena?12 Brentano’s examples include hearing a sound, seeing a colored object, thinking a general concept, loving a dog, and judging that grass is green Since mental phenomena and physical phenomena are both phenomena, things ‘of the mind’ so to speak, to fully understand how psychology is distinguished from the natural sciences, Brentano now faces the third question listed above: what distinguishes mental phenomena from physical phenomena? To give a clear definition of the field of psychology is to answer this last question Examples of physical and mental phenomena may 204