We notice, then, that the sensible quality of a reality that is the sound it makes always implies a movement; it is a quality of a reality that is known only in a movement; without movement there is no sound, and sound is movement. As Aristotle says, ‘Sound is the movement of that which can be moved’ (De Anima II, 8, 420 a 19 ff.). And if sound is movement, it is a relation that is a certain physical contact which is at the source of sound. This contact generates a movement in those realities and consequently in the surrounding air, which is the very movement that reaches the organ of the ear and acts upon it. We see that the role of this intermediary – air – is essential to my hearing sound; without it, no sound can be heard. In other cases, and especially in the case of living realities, the movement of air is also the very ‘contact’ thanks to which the sound is made, as well as the medium that transmits that sound, as in the case of the voice, for example.
So the sound of a reality is a quality it possesses that is only given to me thanks to a physical movement involving another body, or involving air. In this, auditive sensible qualities are like those grasped by the sense of taste, which also require a contact that is one of movement in order for me to know them, and like some of the sensible qualities known by touch, such as harshness and smoothness. However, we notice an order and progression as regards these qualities that are given to me by a contact that is a movement: the contact by which I know a reality’s auditive sensible qualities may be one that is totally exterior to me and indeed not involve me in any way, except in as much as it eventually produces a physical alteration in my ear, thanks to which I know it; knowledge of tactile sensible qualities involves my own body making a physical contact with the other reality; knowledge of the sensible qualities of taste implies a contact that takes place inside my body, in the mouth. As for the senses of smell and sight, we observe that in the case of smell, the movement which results in an odour emanating from a body is a movement that is internal to the reality itself, and that with sight, colours are given to us thanks to light; we might ask, is light a certain movement? We cannot treat that question here; for now we simply note that the sound of a reality is a quality I know of it thanks to a movement that is wholly exterior to me, that does not involve me directly; there is always the intermediary of air. The sensible quality of sound, then, is known thanks to a movement, indeed, is a movement; the movement that it is, is what is received by the ear, and thanks to the vital capacity of hearing becomes a sensitive knowledge for me; I ‘become’ intentionally that sound that I hear.
We might then ask, what does this knowledge give rise to in me? We see that the first question I ask on hearing a sound, is ‘Where does it come from?’. When I hear a sound, I seek, first of all, to know its source, to know where the reality is that is making that sound. Implied in this question is the additional question of how I myself am situated in regard to the reality I hear: where is that reality in relation to me? How far away or how near is it to me? The fact that sound is generated by more than one reality, and one, at least, of those realities in movement, gives a particular sharpness to the intelligence as it asks these questions: if there is movement, is it coming closer or going further away from me? How is it moving in relation to me who am stationary? My location of the source of sound needs to be all the quicker and more accurate given that that source itself is in movement. There is movement somewhere: how could that movement be going to affect me? By the sensible qualities of sound, then, I have a knowledge of the presence of another physical reality and can judge its physical relation to me as regards distance and position.
We can start to see already, therefore, how the sense of hearing is particularly linked to the passions. Hearing a sound provokes a reaction in me: where is the source of that sound? Do I need to move closer to it or distance myself from it? It is precisely in this relation and distance between another physical reality and myself that the passions play a role: my passions are what will propel me towards an effective union with a known good (or a distancing from a reality that my intelligence perceives as an evil or as a threat to a good I already have). However, from the point of view of music, it is hard to see how music affects the passions so much when it does not represent any sensible object as such; it is simply a ‘collection’ of sounds; I am not even interested particularly in the instrument that makes the sound; it is the sound itself that affects the emotions. We need, therefore, to look more closely at the link between sensible knowledge and the passions.