Stoics vs Skeptics: is Knowledge even possible?

Philosophy as a Way of Life
11 min readOct 11, 2021
[image: a pomegranate… or is it?, Wikimedia]

The 2021 edition of Stoicon, the international conference for people interested in Stoic philosophy, has just concluded (online). I presented a somewhat provocative talk bearing the title of this article, just to stir the pot a bit. You see, Stoics (both ancient and modern) more than occasionally have a tendency to slide into dogmatism. And what better antidote for dogmatism than a bit of skepticism?

In particular, I wanted to stimulate some reflection on a crucial debate that unfolded between ancient Stoics and Skeptics, concerning the nature of knowledge. We are talking epistemology, baby! As I will argue in this essay, a good understanding of what constitutes knowledge is not just a matter of interest to professional philosophers, it actually has practical consequences for the way we think and act. And, in this regard at least, the Skeptics had a better argument than the Stoics. Let’s take a look.

First off, what do we mean by “knowledge”? Although there are interesting debates about this in modern philosophy, for the purposes of this discussion I’m going to stick with the time tested definition we owe to Plato (in Meno 98 and Theaetetus 201): knowledge is Justified True Belief, or JTB.

Meaning what? Well, if I claim to know something, according to Plato, three conditions must be met. Most obviously, I have to believe it. It would be weird, for instance, for me to say that I know that my friend Phil lives on Long Island, and yet not actually believe it.

Second, I have to be able, if asked, to justify my belief. Here things get a bit more complicated. How do I know that Phil lives on Long Island? Well, I’ve seen his house, for one. But do I really know that that’s his house? It could be that of a neighbor who temporarily loaned it to him. After all, I haven’t seen Phil’s deed of ownership or rental contract. Nor have I verified that he lives there on a regular basis, since I myself live in Brooklyn, and only rarely go to Long Island.

Things get far worse for less mundane claims to knowledge. If asked, for instance, I might say that I “know” that electrons are subatomic entities characterized by a dual particle-wave nature. But do I really know this? I can’t actually justify this particular belief, other than by referring you to my…

Philosophy as a Way of Life

by Massimo Pigliucci. Practical philosophy, science, pseudoscience & good reasoning. Complete index of articles at