 All mental phenomena have in common, Brentano argues, “that they are only perceived in inner consciousness, while in the case of physical phenomena only external perception is possible” (PES, 70) [“daß sie nur in innerem Bewußtsein wahrgenommen werden, während bei den physischen nur äußere Wahrnehmung möglich ist.” (PES 128)]. According to Brentano, the former of these two forms of perception provides an unmistakable evidence for what is true. Since the German word for perception (Wahrnehmung), literally translated, means “taking-true”, Brentano says that it is the only kind of perception in a strict sense. He points out that inner perception must not be mixed up with inner observation, which would require that one is having a mental act, the act of observing, that is directed towards another mental act, the act observed. Inner perception, on the other hand, must not be conceived as a full-fledged act that accompanies another mental act towards which it is directed. It is rather interwoven with the latter: in addition to being primarily directed towards an object, every mental act is incidentally directed towards itself as a secondary object. When I see a tree, for example, the primary object of my visual experience is the tree. But I am also aware that I am seeing and not, say, hearing or touching the tree; I am, in other words, aware of the fact that I have a mental phenomenon that is directed towards the tree. This is possible because one and the same mental phenomenon, my visual experience, is directed not only towards its primary object, the tree, it is incidentally directed also towards itself as a secondary object. 