Two bodies are said to be touching if there is no spatial gap between some point on the surface of one and some point on the surface of the other. If one of the touching bodies is that of a sentient being, it may be aware of certain properties of the other body: for instance, that it is hot or cold, rough or smooth, wet or dry, hard or soft, sweet or sour.
The sentient being is said to be aware of an object’s sweetness or sourness by taste. (Aristotle attributes our distinguishing taste from touch to the fact that only a part of our flesh is sensitive to flavor.)
The remaining properties the sentient being is said, in common speech, to be aware of by touch. Accordingly, touch appears in the traditional list of senses, with sight, hearing, and so on.
Aristotle remarks that in the case of touch the contraries hot-cold, dry-moist, and hard-soft do not seem to have a single subject in the way in which the single subject of the properties acute-grave and loud-soft is sound, which is perceived by hearing.
This may lead one to say that there are really a number of different senses that are mistakenly referred to as one sense, touch, perhaps because the body of a sentient being must touch an object in order for it to be aware by any of them of that object’s properties.
Or one may say that there is a single subject of the different contraries, namely, a material thing, and that there is only one sense, touch, whereby we are aware of the different properties of which the material thing is a subject. If one takes the latter course, it may appear that touch is the only sense whose proper object is the material world.
Locke, Berkeley, and Condillac
To John Locke, it seemed that “the idea most intimately connected with and essential to body, so as nowhere else to be found or imagined, but only in matter” was the idea of solidity. This idea is received by touch and “arises from the resistance which we find in body to the entrance of any other body into the place it possesses.”
As Locke held it to be by touch that we receive the idea of solidity, the idea essential to body, so George Berkeley, in his Essay towards a New Theory of Vision,held it to be touch alone that directly acquaints us with the external world. He abandoned this view in The Principles of Human Knowledge, maintaining that the objects of touch are as much sensations as are the objects of sight.
Locke regarded solidity as a “simple idea”: “If anyone asks me what this solidity is, I send him to his senses to inform him.” Later philosophers have tried to explain what is involved in the sensation of solidity. Étienne Bonnot de Condillac distinguished it from the sensations of sound, color, and smell, since a person knows his own body by it.
|part of the body|
If a person presses his hand against his chest, his hand and chest “will be distinguished from one another by the sensation of solidities which they mutually give each other.” Thus, involved in the notion of a sensation of solidity is the notion of the recognition as such of a feeling given to a part of the body.
If organic sensations were not localized in the body, a person could never know his own or any other body by touching it, for “it is only with extension that we can construct extension, just as it is only with objects that we can construct objects.”
H. H. Price
H. H. Price carried the analysis a step further. He divided touch “into three distinct types of sensation: contact sensation proper, muscular sensation, and the sensation of temperature.” The perception of solidity involves both contact sensation proper and muscular sensation.
|H. H. Price|
The latter is “essentially a modification of the voluminous life-feeling [that] might also be described as our sense of embodiment.” Muscular strain is felt at a place in the body and as having vectorial character, that is, originating from or tending toward a certain direction.
A person experiences the solidity of something when the resistance he feels on pressing it “is actually felt as coming from within the closed boundary which contact-sensation reveals.... Thus the tactual conception of Matter is strictly speaking tactuo-muscular or contactuo-muscular.”
Local Sign Theory
The analyses of both Condillac and Price specify organic sensations as being localized. As Condillac expressed it, to know its body the child must “perceive its sensations, not as modifications of its soul, but as modifications of the organs which are their occasional causes.”
Condillac cannot explain “how the self which is only in the soul appears to be found in the body ... it is enough that we observe this fact.” The alternatives are either that a person is born with the capacity to locate organic sensations or that he acquires this capacity.
Most philosophers hold the capacity to be acquired, although they differ widely in the accounts they give of how it is acquired; whether by the person’s learning to interpret some feature of the sensation as a sign of its location (the so-called local sign) or in some other way.
Movement and Touch
Perhaps the most important recent contribution to the problem of how touch mediates awareness of its objects was made by David Katz in “Der Aufbau der Tastwelt.” Summarizing Katz’s conclusions, Maurice Merleau-Ponty expresses the crux of the matter as being that “the movement of one’s body is to touch what lighting is to vision....
|Movement and Touch|
When one of my hands touches the other, the hand that moves functions as subject and the other as object. There are tactile phenomena, alleged tactile qualities, like roughness and smoothness, which disappear completely if the exploratory movement is eliminated.
Movement and time are not only an objective condition of knowing touch, but a phenomenal component of tactile data. They bring about the patterning of tactile phenomena, just as light shows up the configuration of a visible surface.”
With the view that the objects of touch are physical objects may be contrasted the view that we are not aware of the object we touch but of a relation holding between our body and that object.
It is a fact that how warm an object feels to an observer depends causally on the warmth of the part of the observer’s body with which he is touching it. We notice the temperature of a hand that is colder or warmer than our own. Aristotle explains this in terms of his theory of sensation as the assimilation in form of the organ to the object.
D. M. Armstrong mentions it, together with the fact that a person can say immediately with what portion of his body he is in contact with an object perceived by touch, in support of his theory that all immediate tactual perception involves perception of a relation holding between the observer’s body and the object he is touching.
As evidence for his theory, Armstrong holds that “hardness and softness as immediately perceived by touch, are obviously relative to the hardness or softness of our flesh.” It is unclear from this evidence whether Armstrong is justified in claiming more than that how things feel to us depends on the condition of the part of the body with which we feel them.
|D. M. Armstrong|