The inside of the ear really vibrates slightly, and thus is modified by the sound it hears- but while the modification of the organ is necessary to sensation, it does not constitute sensation. It is true that, if my ear continually vibrated on its own in exactly the way that it now vibrates when I hear the word “cat” that I would continually “hear” the word “cat”. But this would not be a sensation, but rather an impediment to sensation: it would prevent me from hearing things. While sensation is always a perfection of the sentient being as such, the mere modification of an organ can be an impediment to sensation. Again, it is absurd to think that sensation could be a disease of a sense organ; but the mere modification of the sense organ could be due to some hallucinatory disease. An exaustive account of the physical process of sensation would not suffice to account for what sensation is.