Brentano's Thesis. In an oft-quoted paragraph of Psychology from
an Empirical Standpoint (1874, hereafter PES), offered as a
positive criterion for identifying mental states:
Every mental phenomenon is characterized by what the
Scholastics of the Middle Ages called the intentional (or mental)
inexistence of an object, and what we might call, though not
wholly unambiguously, reference to a content, direction towards
an object (which is not to be understood here as meaning a thing),
or immanent objectivity. Every mental phenomenon includes
something as object within itself, although they do not all do so in
the same way. In presentation something is presented, in judgment
something is affirmed or denied, in love loved, in hate hated, in
desire desired and so on. (PES 88) (Dermot Moran, 'The Inaugural Address: Brentano's Thesis', Proceedings of the Aristotelian Society, Supplementary Volumes, Vol. 70 (1996), pp. 1-27 : 4.)
Very roughly, the idea is that if I am in a state of fear there must be something, existent or supposedly/ imaginedly existent, of which I am afraid : I fear the snarling dog, a bad result in tomorrow's interview, a ghost. My fear must be 'about' something. Equally if I am angry I must be angry 'about' something : the way you have treated me or a slight (even a purely imagined slight). If I am contemplating, my contemplation must be 'about' something.
Mental states have directedness towards an object, as explained, and relation to a content. Brentano's ideas about content are not entirely clear but I think the essential point is that if I fear the snarling dog, the dog or the dog as believed by me to exist, is the object of my fear but that object must be regarded or conceived under a description (I must represent it to myself as potentially dangerous and harmful to me).
This works for a range of examples and is a corrective to the Humean view that emotions are just 'feelings'.
How far does the thesis hold ?
☛ No object
If intentionality involves every mental state being 'about' an object 'under a description', not all mental states easily fit this model. If I am depressed, there need be no object of my depression (real or imagined). I am not depressed 'about' something or need not be; I may just have a pessimistic predisposition to anything that comes to my attention. The state itself has no object.
Again if I enjoy an orgasm, I enjoy a total state of pleasure. The state is caused by the orgasm but is not 'about' the orgasm, nor do I represent the orgasm to myself under a description (a cognitive distraction which would detractive) : I simply enjoy it.
☛ No content
There are in my experience mental states of blankness. When I was recovering from heart surgery I occasionally realised that in the last minute or so I had not been thinking of anything. Sceptically one might say : 'You merely could not remember thinking of anything in the interval'. That's certainly a possibility but my firm impression is that, briefly, I had been conscious but without any presentation, judgement, love, hate or desire (Brentano's examples) going on.
Brentano. F. Psychology from an Empirical Standpoint, ed. Oskar Kraus, English ed. Linda L. McAlister, trans. A.C. Rancurello, D.B. Terrell and L.L. McAlister (London: Routledge, 1973; 2nd English Edition with introduction by Peter Simmons, 1995).
Dermot Moran, 'The Inaugural Address: Brentano's Thesis', Proceedings of the Aristotelian Society, Supplementary Volumes, Vol. 70 (1996), pp. 1-27.