A few additional thoughts on the charge that someone is not being serious.
To say “you are not serious” is probably best understood as expressing the assertion that “I do not take you seriously.” And that assertion justifies me in not engaging with the reasons or beliefs that underwrite your position. I refuse to consider those reasons and beliefs as worthy of any consideration, or any respect. They—and you—can be dismissed out of hand. I stand on solid ground, you have no standing at all. Whatever reasons you think you have for acting that way, or believing what you say you believe, are frivolous and insubstantial.
The further twist (in some cases) is that “your stated reasons” cannot (because so insubstantial) really be the reasons (the motives, the causes) for your behavior. You are not “serious” in offering that account of your action because any thoughtful person would recognize how flimsy, how implausible, those reasons are. You are being disingenuous, pretending to be offering a sincere account of why you act this way or believe this thing, when you are in fact dissembling.
And you are dissembling either because you are not willing to publicly embrace (affirm) your real reasons/motive or because you are an unreflective person, totally out of touch with your real reasons and motives. Or, the other way around, you are pretending to believe something that you can’t really believe—and that your actions show that you don’t really believe. You are stubbornly holding onto an intellectual position the consequences of which cannot be lived. (This is Gaita’s response to skepticism.)
My thoughts about my non-serious grad school colleagues took, I think, this form: they were unserious because they were avoiding (for any number of reasons) actually thinking about what they were up to and where they were trying to get to. It was too scary to take stock, to clearly consider what they desired, and then to think about what actions would move them closer to the realization of those desires. Better to live in a haze than to commit wholeheartedly to something they might fail to achieve. A kind of self-protective diffidence.
Flipping back to the one who makes the charge “you are not serious.” What is withheld is respect for the other person. I don’t respect your choices, your actions, or your stated reasons/motives when I declare you are not serious. And that means I take myself off the hook from any effort to empathize, any effort to understand who you are and what moves you to act and believe as you do. The charge is dismissive in ways that border on cruelty—and the charge is also, I am insisting, in bad faith when trotted out in any dialogic situation. It shuts down any possibility of an exchange of views, of an opening up of minds on either side of a disagreement. To say “you are not serious” is simply a form of dogmatism. I am right, you are wrong—and so wrong that you can’t seriously believe what you are saying. You can only be saying it disingenuously or out of lamentable (but blameworthy) ignorance.
It is this element of contemptuous dismissal that bugs me so much about the way philosophers use the word “serious.” And so proudly, so self-righteously, as if it was the ultimate refutation of the other’s position. I really do not think that non-philosophers retreat to a charge of “non-seriousness” as often as philosophers do.