[UPDATE: revised August 30 2013]
The situationist challenge relies on the claim that we lack sufficient evidence to believe that global traits of character as they are understood in virtue theory – whether moral or epistemic – are achievable for a large proportion of people. This claim is often abbreviated into the much stronger claim that global character traits do not exist, but a careful review of the literature reveals that this is only an abbreviation. In response to the abbreviated claim, it might be argued that global traits of character do exist, and that, in fact, we have strong empirical evidence that they exist from the enormous literature on the so-called “Big Five” or Five Factor Model (McCrae & John 1996), which posits that the five dominant dimensions of personality differences are openness, conscientiousness, extroversion, agreeableness, and neuroticism.
Doris (2002) and Prinz (2009) were the first to consider this argument in detail, and also the first to reject it. Several difficulties beset the appeal to the Big Five. First, the number of factors is arbitrary: the statistician decides a priori how many factors to include. This means that, depending on one’s arbitrary choice, the number of basic character traits can toggle from five down to four or up to seven. But as Quine taught us, “No entity without identity” (1969, p. 23): unless we can count something, we should not include it in our ontology. The traits “revealed” by factor analysis cannot be counted (or, more precisely, can be counted up to whatever n one likes), so at least naturalistically-inclined philosophers should look at them askance.
Second, Big Five traits are best understood as broad generalizations about behavior rather than as character traits as virtue theorists conceive them: they do not license the prediction of particular behaviors, thoughts, deliberative strategies, perceptual sensitivities, or emotional reactions. Someone who is very high in agreeableness may nevertheless act aggressively. Someone who is very low in extroversion may nevertheless feel comfortable in a social setting. Someone who is very high in neuroticism may fail to perceive a vaguely disturbing episode as a threat. Someone who is very high in openness may nevertheless fail to deliberate responsibly about another person’s suggestion. Virtues as traditionally conceived are meant to license the prediction and explanation (as well as the evaluation – a point I turn to next) of particular cognitions, affects, and behaviors. Big Five traits at best license explanations but not predictions.
Third, as Miller (forthcoming) points out in his paper on the Big Five and situationism, these traits appear to be largely heritable (McCrae et al. 2000, p. 174-5), whereas character traits are meant to be acquired during the agent’s lifetime. One could give up the idea that agents are responsible for their own character, which would in turn allow one to give up the claim that virtues and vices are acquirable, but it’s hard to find virtue theorists who are willing to do this. Homer might be one: nobility seems to be largely heritable in the Iliad. Nietzsche might be another. Knobe & Leiter (2007) argue that he thinks character traits are not just heritable but genetic, though I (forthcoming c) am unconvinced.
Fourth, the Big Five are not normatively loaded in a way that would help in making virtue (or vice) attributions. For instance, it’s neither a virtue nor a vice to be extroverted. One might think that some of the factors, or at least some of their sub-factors, would be normatively adequate, but as Miller (forthcoming) has convincingly argued, this does not appear to be the case. In fact, there is a historical reason for this. When personality psychology was being developed in the first half of the twentieth century, the same zeitgeist that inspired the logical positivists to reject normative language as non-truth-apt (Ayer 1936) also led prominent personality psychologists such as Allport & Odbert (1936) to eschew evaluative language in their theories of personality. For instance, evaluative terms (‘stupid’, ‘wicked’, ‘outstanding’), terms that describe enduring sentiments (‘sad’, ‘angry’), and terms that are judged by the theorist to be response-dependent (‘charming’, ‘dangerous’, ‘disgusting’) were not included in the foundations of the Big Five. It should come as no surprise, then, that the Big Five are normatively incommensurable with virtues or vices as ethicists and epistemologists understand them.
For these reasons, among others, literally no one has invoked the Big Five to defend virtue theory. However, one might think that judgment was passed too quickly. As I mentioned above, the number of factors is chosen by the statistician, and it turns out that when a sixth factor is included, it tends to look more promising. Based on factor analysis of lexical similarities across a variety of languages, Lee & Ashton (2004), for instance, posit that the sixth factor is honesty / humility. But Lee & Ashton (2004), like Allport & Odbert (1936), intentionally exclud highly evaluative terms from their analysis, so the same problem that plagues the Big Five also infects their Big Six. Saucier (2009), by contrast, explicitly set out to construct a Big Six taxonomy that included evaluative terms. The six factors in this model are Conscientiousness, Negative Valence (cruelty, corruption, disgust, wickedness, evil, and insanity), Agreeableness, Emotional Resiliency (lack of depression, cowardice, fear, frustration, gloom, and sadness), Gregariousness (similar to extroversion), and Originality (intelligence, talent, admirability, wisdom). This research program is only in its infancy, so it’s hard to say how successful Saucier’s version of the Big Six taxonomy will be, but early indications suggest that it is empirically better supported than the Big Five. More importantly for virtue theory, its intentional inclusion of evaluative, sentimental, and response-dependent terminology makes it a better candidate for identifying virtues and vices – including intellectual virtues as vices such as intellect and originality.
 Others include Alfano (2013a), Kamtekar (2004), Kristjánsson (2012), Miller (forthcoming), and Slingerland (2011).
 As with the Big Five, the factors in this model are orthogonal to one another. It may therefore come as a surprise to ethicists familiar with the unity of virtue thesis that there are multiple positive factors, which are uncorrelated with one another) but only one negative factor. This could be taken to suggest that, at least in folk psychology, the unity of vice is considered more likely than the unity of virtue.
The Big Six (Saucier 2009) Personality Structure
Unfortunately, all of the other problems with the Big Five remain unabated. There is as yet no evidence that Big Six personality traits can be acquired. Nor is there evidence that Big Six traits could license the prediction of particular behaviors, thoughts, deliberative strategies, perceptual sensitivities, or emotional reactions. The Negative Valence dimension does correlate with having at least once in one’s lifetime engaged in risky behaviors such as drunk driving, bar brawls, shoplifting, vehicle theft, assault, and delinquent gang activity (Simms 2007), but a single action does not constitute a vice, and people who are high in Negative Valence may never engage in or even contemplate any such activities. I conclude that, as yet, neither the Big Five nor the Big Six personality taxonomies lend any comfort to virtue theory in its struggle against ethical or epistemic situationism.
 Others include Alfano (2013a), Doris (2002), Kamtekar (2004), Kristjánsson (2012), Miller (forthcoming), and Slingerland (2011).