In the contemporary West, it is taken for granted that sexual preferences—that is, what things people find sexually appealing—fall into a few discrete categories, which are called sexual orientations. Invariably, heterosexuality and homosexuality are considered sexual orientations (although some consider the word "homosexuality" stigmatizing for historical reasons). Usually, bisexuality is included. Many other extensions to this taxonomy exist, although none are popular among laymen. Among these extensions are a four-orientation model in which asexuality is included as a fourth orientation; the Kinsey scale, in which there is "Exclusively heterosexual with no homosexual", "Exclusively homosexual", and five intermediate points (Kinsey, Pomeroy, & Martin, 1948, p. 638); an added distinction between "tops" and "bottoms" (insertive or dominating versus receptive or submissive); a dual-axis model in which preferences for age are distinct from preferences for gender (Seto, 2012); and the Klein grid, which comprises 27 seven-point items (on gay–straight axes) organized into seven features and three time-points (Weinrich et al., 1993).

So, how well are real people's real sexual preferences described by these taxonomies? In everyday life, we rarely ask this question—we assume that the gay–straight dichotomy or gay–bi–straight trichotomy is correct and thence do all our reasoning about people's sexual preferences. Should these models be wrong, it is easy to see how great harm could arise from slavish application of them, from trying to pound square pegs into round holes. I need not provide any anecdotes about the misery people undergo when they feel unsure about their sexual orientation: popular media and likely the reader's own life are full of such anecdotes. How much more inescapable this suffering would be if the root problem were not mere ambiguity about which sexual orientation one belonged to, but the nonexistence of a sexual orientation that fits! The situation could then only be resolved with stoic apathy, denial of one's own feelings, or the invention of yet another sexual orientation. (As if we needed another letter added onto "LGBTQAOMGWTFBBQ".)

I'm tempted to claim that sexual orientation, considered as a psychological theory, is wrong. But I can't, because, as I was saying earlier, sexual orientation isn't any one theory or model; it's more like a big family of models with the lay dichotomy as common ancestor. The family as a whole can't be falsified. Faced with falsificatory evidence for any one model, one could extend the model into a new one that can handle the new evidence. Falsification is yet more difficult because sexual orientation, although often employed in an explanatory fashion (particularly by laymen), is more descriptive than explanatory: it says a lot more about the exact phenomena of interest (sexual attraction and behavior) than about any supposed causes. A careful thinker wouldn't claim that Joe has sex with Bob because Joe is gay; they would instead attribute the causal power to whatever they think causes male–male sexual attraction and behavior to begin with, and say that the attraction that led Joe to have sex with Bob is part of what constitutes Joe's homosexuality. There are then few causal chains within these models to test, and the only way they're accountable to empirical reality is that they have to include everybody, or at least, every sexual-preference pattern that can be found in more than a dozen people. The only other constraint on these models is that they have to be models, in the sense that they need to make only finitely many distinctions and they need to have halfway-coherent theories behind them.

There exists a more sophisticated philosophy for scientific models, which is to assume that all models are, in the final analysis, false, and change the focus from finding a correct model to finding the most useful model (see Arfer & Luhmann, 2015, for a related discussion). How exactly usefulness should be measured is, of course, context-dependent. It then becomes difficult to talk about how good a model is in abstract terms. A model that's excellent for one purpose could be poor for another. I think, however, that the onus is very much on the proponents of sexual orientation to demonstrate it is useful for anything other than breeding confusion and hatred among ordinary people.

At any rate, I can't falsify sexual orientation. The most I can do here is to enumerate some potential problems for any sexual-orientation taxonomy. These gotchas will mostly be ways sexual preferences can be diverse, which may remind you of the lists of non-reproductive sexual practices in the previous chapter. (But I'll give much less attention to animals than last time, because, for reasons that aren't clear to me but might just be differences of discipline (e.g., ethology versus sociology), scientists are much less hasty to classify the sexual preferences of animals than of humans.) Some are more specifically problematic to one model than another. Taken together, though, they're strong reason not to put too much faith in the idea of sexual orientation.