The metaphor of triangulation appears first in Three Varieties of Knowledge in Davidson’s discussion of radical interpretation. Interpretation must adopt a compositional approach in the determination of meaning. That is, it must recognise the interconnectedness of attitudes and behaviour; in turn attributes and behaviours are constrained by normative principles of rationality.
The holistic consideration is married with an externalist position in which attitudinal content determined by the interconnectedness of attitudes and behaviour is seen in the light of its dependence on causal connections between attitudes and objects in the world. Attitudes can only be attributed and attitudinal content determined through a triangular structure. The triangle is based on the connection between two creatures, and a creature and her connection to a set of common objects in the world.
The content of attitudes is causally fixed by the objects of those attitudes; in turn, the cause of an object is reflected in the cause of those attitudes. Identifying beliefs involves a process of triangulation, whereby the position of an object is determined by taking a line from each of two already known locations to the object in question — the intersection of the lines fixes the position of the object. Similarly, the objects of propositional attitudes are fixed by looking to find objects that are the common causes, and so the common objects, of the attitudes of two or more speakers who are capable of observing and responding to one another’s behaviour.
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. If we project the incoming lines
outward, their intersection is the common cause. If the two people note each others’ reactions (in the case of language, verbal reactions), each can correlate these observed reactions with his or her stimuli from the world. The common cause can now determine the
contents of an utterance and a thought. The triangle which gives content to thought and
speech is complete. But it takes two to triangulate. Two, or, of course, more. (Davidson
The metaphor of triangulation is extended by Davidson to explain the interconnectedness of knowledge of oneself, of others, and of the world. It is not possible, Davidson claims, to have knowledge of oneself without having knowledge of the other two concepts of others and of the world.
Triangulation has the implication that interpreting attitudinal content must proceed in conjunction with interpreting objects, be they in the world or in language, for otherwise we would not understand the cause of the belief in question. In the case of language, this takes the form of interpreting linguistic utterances or sounds. Thus, if we cannot understand an utterance we are unable to attribute attitudinal content. For Davidson, this means that non linguistic animals are incapable of thought, since thought is the possession of precisely that attitudinal content disclosed by a linguistic utterance.