How Do You Know That You Know?

You claim to know something. Perhaps you know that the Earth orbits the Sun, or that 2 + 2 = 4, or simply that you exist. But consider this question:

You need some criterion - a method, standard, or test that separates genuine knowledge from mere opinion or error.

But now a deeper question arises:

This is the Problem of the Criterion, one of the oldest and most devastating challenges in philosophy. It was posed by ancient skeptics and revived by philosophers like Roderick Chisholm in the 20th century. And it remains unsolved.

When you claim to know something, you can always be asked: “How do you know?” You might answer with evidence, reasoning, or a method. But then comes the next question: “How do you know THAT is reliable?”

Watch the regress unfold. Each answer generates a new question, each justification requires its own justification:

This is not just philosophical pedantry. The regress reveals a genuine structural problem: justification cannot get started. Every step backward needs another step, forever.

When pressed to justify our criterion for knowledge, we face exactly three options. All three are problematic. This is sometimes called Agrippa's Trilemma or Munchhausen's Trilemma.

No matter which horn we grasp, we seem to lose our grip on knowledge. The ancient Pyrrhonian skeptics used this argument to advocate for suspension of judgment (epoche) - simply refusing to commit to any belief about how things really are.

One tempting escape from infinite regress is to argue that our system of knowledge is coherent - beliefs mutually support each other. But this creates a circle.

Explore different circular structures. Notice how each element depends on others, with no independent foundation:

The problem with circular reasoning is severe: a consistent fiction could be equally coherent. Imagine an elaborate fantasy world with perfectly consistent internal logic. Coherence alone cannot distinguish it from reality.

Philosophers have identified two broad strategies for approaching the problem. Neither fully solves it, but they represent fundamentally different starting points.

Roderick Chisholm, who revived interest in this problem in the 20th century, argued for particularism: we should trust our paradigm cases of knowledge and build criteria from them, rather than waiting for perfect methodological foundations.

But critics point out that particularism merely pushes the problem back: which paradigm cases do we start with?Different traditions offer different examples. Without a criterion, we cannot adjudicate.

Throughout history, philosophers have proposed various criteria for genuine knowledge. Each faces its own version of the problem. Select a criterion and watch it face the skeptical challenge:

The pattern is always the same: any criterion we propose can be questioned, and the question cannot be answered without either assuming another criterion (regress) or assuming the criterion itself (circularity).

The Pyrrhonian skeptics of ancient Greece developed the Problem of the Criterion into a powerful tool for inducing suspension of judgment. They would engage opponents in dialogue, systematically exposing the groundlessness of every claim to knowledge.

Try defending your knowledge against the skeptic. Choose your responses and see where each path leads:

The skeptic is not trying to prove you wrong - they are showing that you cannot prove yourself right. The goal is not negative dogmatism but peaceful suspension, living without the anxiety of needing certain foundations.

Philosophers have grappled with this problem for over two millennia. None has produced a universally accepted solution, but each response illuminates different aspects of the challenge:

The Problem of the Criterion is not just an academic exercise. It has profound implications for how we think about science, disagreement, and the limits of reason.

We know more than we can prove.
And perhaps that is enough.