Lovejoy, A.O. (1929). The Revolt against Dualism. LaSalle, Ill.: Open Court.
Steven Lehar had the following to say about Lovejoy:
The Revolt Against Dualism is Lovejoy, a fellow from the early 1900s, and a "critical realist", which is one step better than a naive realist, but is not a full-blown representationalist. As I summarize here:
The critical realists all agreed on the fact that the sense data are independent of the object of perception itself. However the question of whether the sense data are part of the mind, or whether they are aspects of the external object is one on which critical realists differed in subtle ways. In a book on critical realism by a consortium of authors (Drake et al. 1920) Lovejoy, Pratt, and Sellars claim that the sensa are completely "the character of the mental existent ... although its existence is not given" whatever that might possibly mean, while Drake, Rogers, Santayana, and Strong agree that the data are characteristic of the apprehended object, although "the datum is, qua datum, a mere essence, an inputed but not necessarily actual existent. It may or may not have existence." (p. 20-21 footnote), whatever that might possibly mean! So the critical realists solved the problem of sense-data by defining a unique kind of existent which may either be part of the external object, or of the internal mental state, but in any case it has a status of quasi-existence which supposedly escapes the problems inherent in identifying it explicitly as either an external or internal entity. Epistemological confusion inevitably leads to a confused philosophy.
More on Lovejoy, when he attacks Bertrand Russell's true representationalism:
Lovejoy's (1930 p. 227-249) response to Russell's epistemological dualism is typical. Lovejoy does not argue on logical grounds that percepts cannot be in our heads, but argues instead that there are alternative explanations which, however improbable, at least leave the door of doubt open a tiny crack. One such possibility is a projection theory, that the patterns of electrochemical activity in our brain get somehow projected back out into the world. Another possibility is that although perceived objects are not in physical space, "it does not follow that they are in our heads; they might ... be neither in our heads nor where the 'scientific objects' are, but in some other situation in physical space." (Lovejoy 1930 p. 228) His third argument is that it has never been proven that `being known' is necessarily equivalent to `being in our heads'; and finally Lovejoy argues that the question whether percepts are in our heads is not the same as the question whether perceiving and awareness are physical processes, and that he rejects the former but accepts the latter. What is curious about these arguments is that Lovejoy feels no need to commit to any one of his proposed alternatives. Lovejoy does not profess a projection theory, but merely argues that it is not self-evident that it is untrue. If percepts are not in our heads, Lovejoy does not propose where else they might be. He does not explain how anything can be known that is not explicitly represented in our physical brain, nor how the physical processes underlying perception and consciousness could be anywhere other than in our brain. This therefore is not a refutation of Russell's causal theory of perception, but merely an expression of Lovejoy's opinion that Russell's theory seems so incredible to him, as to be on a par with those other incredible hypotheses.