In light of ongoing discussions here and at Theos Project, I thought I’d summarize an essay by American philosopher Donald Davidson on the subject of knowing one’s own thoughts and the thoughts of others. Davidson’s position is quite consistent with Tomasello’s use-based theory of language acquisition and related empirical findings. It’s perhaps also compatible with Gadamer’s hermeneutics, though they come from very different philosophical traditions. I know, for the most part, what I think, want, and intend, and what my sensations are. In addition, I know a great deal about the world around me, the locations and sizes and causal properties of the objects in it. I also sometimes know what goes on in other people’s minds. In these first three sentences Davidson identifies the “Three Varieties of Knowledge,” the interrelatedness of which he explores in his 1993 essay of that name.
Davidson acknowledges that probably the most common approach is to assert the primacy of self-knowledge because of its directness and relative certainty, then to derive knowledge of the external world from it, and knowledge of other minds from observing others’ behavior. He wishes to show that this approach is wrong. No one form of knowledge can be derived from either of the others, says Davidson; rather, all three are dependent on each other.
First he addresses the negative situation, which essentially comes down to this: it’s possible that someone can, without realizing it, believe a falsehood or interpret a subjective experience incorrectly. Consequently, no amount of knowledge of the contents of one’s own mind insures the truth of a belief about the external world, [and] no amount of knowledge about the external world entails the truth about the workings of a mind. If there is a logical or epistemic barrier between the mind and nature, it not only prevents us from seeing out: it also blocks a view from outside in. Further, if our experience of other minds is derived only by inference from observing their behavior, we have no basis for asserting that others’ minds are anything like our own.
Belief is a condition of knowledge, says Davidson: if I say “the snow is white” I can also say “I believe that the snow is white,” even though the first statement refers to the world while the second refers to my state of mind. In order to believe something it’s not enough to discriminate between features of the world and to act accordingly. A sunflower that aims itself at the sun isn’t acting from a belief, nor if it aims at an artificial light has it made an error in judgment. Having a belief demands in addition appreciating the contrast between true belief and false… Someone who has a belief about the world — or anything else — must grasp the concept of objective truth, of what is the case independent of what he or she thinks. And where do we get this concept of truth that underlies our idea of true and false belief? Here Davidson follows the later Wittgenstein: The source of the concept of objective truth is interpersonal communication. Thought depends on communication.
In order to understand what someone says, I need to know both what she means and what she believes about this meaning. I therefore have to assume that the speaker is logically coherent and consistent — rational — and that she is responding to the same features of the world as I am. This is the unspoken compact binding the speaker’s utterances to her beliefs, and her beliefs to my beliefs. Why should this tacit and tentative interpersonal agreement, based not on fact but on something like charity, form the basis for objective truth?
Like the sunflower orienting toward sunlight, humans discriminate between features of the world. Language assigns names to the discriminatory criteria: light/darkness, snow/rain/hail, etc. If I try to understand someone who speaks a language that’s different from my own, I have to figure out whether her discriminatory criteria match my own. And I can’t do that merely by comparing languages; I can only do it by attending jointly with the other person to various stimuli in the world, and then seeing if her words for these stimuli match up with mine. The consistencies in discriminatory criteria for parsing the world need to match up with both my linguistic categories and the speaker’s.
For until the triangle is completed connecting two creatures, and each creature with common features of the world, there can be no answer to the question whether a creature, in discriminating between stimuli, is discriminating between stimuli at the sensory surfaces or somewhere further out, or further in. Without this sharing of reactions to common stimuli, thought and speech would have no particular content — that is, no content at all. It takes two points of view to give a location to the cause of a thought, and thus to define its content. We may think of it as a form of triangulation: each of two people is reacting differentially to sensory stimuli streaming in from a certain direction. Projecting the incoming lines outward, the common cause is at their intersection. If the two people now note each other’s reactions (in the case of language, verbal reactions), each can correlate these observed reactions with his or her stimuli from the world. A common cause has been determined. The triangle which gives content to thought and speech is complete. But it takes two to triangulate.
Until a base line has been established by communication with someone else, there is no point in saying one’s own thoughts or words have propositional content. If this is so, then it is clear that knowledge of another mind is essential to all thought and all knowledge. Knowledge of another mind is possible, however, only if one has knowledge of the world, for the triangulation which is essential to thought requires that those in communication recognize that they occupy positions in a shared world. So knowledge of other minds and knowledge of the world are mutually dependent; neither is possible without the other.
The stimuli that cause our verbal responses to the world are also what those verbal responses mean, as well as the content of our beliefs about the world. We might jointly triangulate on the same wrong beliefs; however, because we arrive at an interpersonal agreement regarding meaning and belief makes it very likely that we’re right about our basic perceptual beliefs and our general picture of the world. It’s difficult to isolate a particular belief as true or false, however, because knowledge of the world, of one’s own beliefs, and of others’ beliefs are irreducibly interdependent and holistic. We can identify invariants across all three points of the triangle, but we cannot regard any one point as determinate, independent of its relationship to the other points.
A community of minds is the basis of knowledge; it provides the measure of all things… The thoughts we form and entertain are located conceptually in the world we inhabit, and know we inhabit, with others. Even our thoughts about our own mental states occupy the same conceptual space and are located on the same public map… The objective and the intersubjective are thus essential to anything we call subjectivity, and constitute the context in which it takes form… If I did not know what others think, I would have no thoughts of my own and so would not know what I think.