Intentionality and Psychologism
Brentano’s thesis is that every mental phenomenon is directed to an Object distinct from itself. It has an extra-mental correlate—the thing thought about or perceived or desired or loved or hated, etc. This entity may or may not exist (but I will ignore the latter case from now on). On the one hand, we have the mental phenomenon itself, on the other, the Object of the phenomenon. What this Object is can be quite various; it is certainly not to be identified with an existent material thing. It can be viewed as a theoretical entity whose existence (sic) follows from the nature of the mental: objects, properties, and states of affairs will be included, but also anything else called for by the mental phenomenon in question. There is nothing in Brentano’s formulation that requires the Object to be part of common sense, or even cognitively available to the subject. One question we can ask is what counts as a mental phenomenon for Brentano: does he mean a whole mental state like a judgment or desire, or does he mean to include constituents of such a state? That is, do concepts also have intentionality? I mean “concept” in the broadest sense that corresponds to meaning or Frege’s Sinn not just mental representations of properties—thus including quantifier concepts, connective concepts, modal concepts, ethical concepts, logical concepts, and so on. Do all of these have an extra-mental correlate as their Object? I propose that we take Brentano’s thesis literally and apply it to these mental phenomena too; indeed, we might take the Object of a whole mental state to be a function of the Objects corresponding to the constituents of that state. If so, we are going to need a specification of which Object such a mental primitive is directed towards (compare Frege’s generalized theory of reference).
I said that each mental phenomenon must have an extra-mental correlate, but of course this is wrong construed completely generally, since some mental states take other mental states as Objects, either in oneself or in others. I can believe that I’m in pain and I can deplore your political beliefs, for example. But these mental states must themselves be about something other than themselves, so that my mental states directed towards them will inherit their Objects. In fact, a potential regress lurks here: if the mental state that my mental state is about itself has a mental state as its Object, then we will need a further Object to be the Object of this mental state. According to the intentionality thesis, then, such chains of mental states will bottom about in a non-mental Object. So we may as well say that every mental state ultimately has a non-mental Object as correlate. But we have still not said what these Objects are—what is it that every mental phenomenon must bring with it as a distinct entity? Here our options are wide open; so far we have only a schema not an articulated theory. We might favor existing material objects and their properties, or we might prefer some sort of peculiar “intentional object”; and when it comes to quantifiers and connectives we can wax more abstruse—maybe the Objects here are Fregean functions, taken either in extension or intension. We might even suggest that the Object of the concept and is the truth table corresponding to conjunction. Nothing in Brentano’s formulation stipulates that the subject should be conscious of the Object, let alone be in a position to define or articulate it: Brentano doesn’t say the required Object must be known by the subject—it merely has to be. So the Object of and could be a set of introduction and elimination rules, or a functional role, or even a brain state—as long as it is distinct from the concept and itself (it could even be an idea in the mind of God). The essence of the thesis is just that every mental phenomenon is directed to an Object of some sort as part of its very nature. In principle it could be abstract, fictional, or recondite.
Suppose I am thinking about physics and contemplating the law of gravity: I am deploying the concept the law of gravity. What is the Object of my mental act? Surely it is the law of gravity, construed as a non-mental thing. So natural laws can be Objects of mental states too. I could be wrong about such laws, but they would still be the Objects of my thought (compare perception and material objects). Or suppose I am thinking about morality and contemplating the Golden Rule: isn’t the Object of my thought precisely the Golden Rule? But then it must be distinct from my contemplation of it, by Brentano’s thesis; and the same for any moral thought—the value that is thought about must be distinct from the thinking about it. The concept good must have an Object that is not identical to that concept, which we might think of as the property of being good (or the Form of the Good if we follow Plato). Not that we are constrained to such entities by Brentano’s thesis alone, but they would be examples of the kind of thing that is required by the thesis. What matters is that they are not mental. For the thesis is that the mental is always inextricably bound up with the non-mental. Now let’s consider logical reasoning: I am thinking logically about a problem and I engage in a bit of logical inference, say by modus ponens. What is the Object of my mental process? The answer is modus ponens (or something else if we want to get eccentric about it, say the Andromeda galaxy, but let’s stick to modus ponens). But this logical law must be non-mental in order to be the Object of my mental act of employing it. Therefore psychologism is false. The law can’t be identical to the mental process I am engaging in, since that process needs an extra-mental correlate to be its Object. Thus Brentano’s thesis refutes psychologism about logic. The mental process of logical reasoning must be about something, but this something can’t be itself, so logical laws can’t be identical to logical reasoning. Of course, we might have come to this conclusion on other grounds (see Frege), but it is striking that the relatively anodyne claim of universal intentionality should yield such a powerful result. There seems to be a strong tendency to psychologize logic, but this is incompatible with the principle that all mental phenomena need a non-mental Object. We simply need to extend Brentano’s thesis from the obvious cases to take in such mental phenomena as logical reasoning: because inference too has intentionality, like thinking about natural laws and ethical precepts. The mental process of inferring must itself be about something, and that something is logic. If we were to try to reduce logic to logical reasoning (i.e. adopt psychologism), then we would face the question: “But what is logical reasoning about?” It can’t be about itself, so it must be about something else, and that something is surely logical reality (whatever exactly that is). A sensory perception must be about something, but that something can’t be itself, so there has to be something non-mental involved (e.g. a material object); logical reasoning obeys the same rule, so that psychologism is excluded. Psychologism with respect to logic is really a species of idealism, and Brentano’s thesis cuts against idealism, since mental states must be directed towards extra-mental entities of some sort (not even Berkeley thinks that ideas of sense are representations of themselves). At the least we need something like intentional objects, which are not mental (what they are is hard to say). So Brentano’s thesis has metaphysical teeth precisely because it connects the mental with the non-mental. His insight was that the mind is essentially a representing thing, but that it doesn’t represent itself qua mind: it opens out onto a wider world (though this world might not exist). In contrast, the body is a non-representing thing, making no reference to anything beyond itself (it makes no referenceat all). Idealists (including proponents of psychologism) make the mistake of assimilating the mind to the body, ironically enough, ignoring the way the mind reaches out beyond itself; but once we take the measure of intentionality we see that there cannot be only the mind (there could be only the body). If there is mind, there must be something other than mind, such as objects, properties, states of affairs, truth functions, natural laws, ethical values, and laws of logic. It isn’t that the existence of mind entails the existence of the commonsense world (we haven’t refuted skepticism), but there has to be a level of reality (there is no other term) beyond the mental as such. There has to be something non-mental for the mind to latch onto even if it is just those elusive intentional objects (or possibly Platonic forms).
 It is sometimes thought that pain is a counterexample to Brentano’s thesis, since it has no Object beyond itself. There are two cases to consider: emotional pain and physical pain. In emotional pain the extra Object will be whatever is the cause or occasion of the pain—the rejection, loss, treachery, or perfidy, as the case may be. In physical pain it will be the part of the body where the pain is felt to occur (which may not actually exist). No pain is ever completely dissociated from accompanying allusions to distinct Objects.
 The question of why the mind is intentional is left open and is difficult to answer. Could there be a type of mind, not necessarily conceivable by us, that is not intentional? What function does intentionality serve, if any? Does it have anything to do with information processing? What is its physical basis in the brain? Does it derive from any more basic feature of the cosmos? What is its connection to consciousness? How did it evolve? It is certainly something remarkable and not present in non-mental reality, but we know little about it beyond its evident existence.