Gareth Evans (12 May 1946 – 10 August 1980) was a British philosopher at Oxford University during the 1970s.
Evans was one of many in the UK who took up the project of developing formal semantics for natural languages, instigated by Donald Davidson in the 1960s and 1970s. He co-edited Truth and Meaning (1976) with John McDowell on this subject. He also wrote a paper, "The Causal Theory of Names" (1973), which heavily criticized certain lines of the theory of reference that derived from Kripke's Naming and Necessity (1972/1980) and work by Keith Donnellan.
A one-page paper in Analysis, "Can There Be Vague Objects?" (1978), drew dozens of papers in response and is now considered a key work in metaphysics.
From Russell's work, Evans also draws the point that some of the thoughts one has (thoughts about objects one is perceiving, for example) are such that if their object did not exist it would not be possible to think that thought at all. These he calls Russellian thoughts.
He then claims that a certain version of the new theory, which he calls the Photograph Model of mental representation (1982, p. 78), violates Russell's Principle. According to the Photograph Model, "the causal antecedents of the information involved in a mental state... are claimed to be sufficient to determine which object the state concerns" (1982, p. 78). (The view is so named because it is similar to the view many people take on how a photography comes to be about something.) Thus, on the Photograph Model, contrary to Russell's Principle, one may have a thought about some object without discriminating knowledge of that object, just so long as the mental state is caused in the appropriate way (for example, perhaps by some sort of causal chain that originates with the object).
Evans argues that any causal theory, like that of the Photograph Model, must be restricted in certain ways: it is necessary to consider, one by one, the various kinds of Russellian thoughts people can have about objects, and to specify in each case what conditions must be met for them to meet Russell's Principle--only under those conditions can one have a thought about a specific object or objects (a singular thought).
In particular, Evans discusses at length what he calls the Generality Constraint. Evans states it thus:
...if a subject can be credited with the thought that a is F, then he must have the conceptual resources for entertaining the thought that a is G, for every property of being G of which he has a conception (1982, p. 104).
The Generality Constraint, according to Evans, is intended to capture the structure that there is in thought. As Evans puts it, "The thought that John is happy has something in common with the thought that Harry is happy, and the thought that John is happy has something in common with the thought that John is sad" (1982, p. 100). The Generality Constraint requires that if one is to have a thought (that John is happy, for example) about an object (John), then one must be able to conceive of the object (John) as having different properties (such as being sad).
He also defends a reading of Frege, derived in part from Michael Dummett's work, according to which Frege's notion of sense is not equivalent to a description, and indeed remains essential to a theory of reference that abandoned descriptivism (1982, §1.3).
He considers first demonstrative reference, where one speaks or thinks about an object visible in one's vicinity. He argues that these presuppose, among other things: having a correct conception of the kind of object that it is; the ability to conceive of it and oneself as located in an objective space, and to orient oneself within that space; that one must move smoothly through time and space and be able to track the object's movements continuously in perception.
He next considers reference to oneself and then reference by way of a capacity for recognition: one's ability to (re-)identify an object when presented with it, even if it is not available at present. Evans famously considers the phenomenon of Immunity to Error Through Misidentification--a phenomenon of certain types of judgment in which one cannot be wrong about which object the judgment is about by misidentifying it (see his 1982, especially §6.6 & §7.2). This phenomenon may be exemplified by the incoherence of the following judgment (upon feeling pain): "Someone seems to be feeling pain, but is it I who is feeling the pain?". While this phenomenon has been noticed by philosophers before, Evans argues that they have tended to think that it only applies to judgments concerning oneself and one's conscious experiences, and so they have failed to recognize that it is a more general phenomenon that can occur in any sort of demonstrative judgment. Furthermore, philosophers such as Ludwig Wittgenstein (in his Blue and Brown Books [1958]) and Elizabeth Anscombe (in her "The First Person" [1975]) have wrongly concluded that such cases show that the first-person pronoun "I" does not refer to anything.