What is the problem of the criterion in skeptical philosophy?

In skeptical philosophy, the problem of the criterion refers to the challenge of establishing a justifiable standard or "criterion" by which to measure the validity of knowledge claims or judgments.12

The problem arises because any proposed criterion requires its own justification to be considered valid. This leads to a logical dilemma:

• Infinite Regress: If you justify a criterion with another criterion, you must then justify that second criterion, leading to an endless chain of justification.12
• Circular Reasoning: If you use a criterion to justify itself, the argument becomes circular.1
• Arbitrary Stopping: If you simply stop the process of justification without further proof, the criterion is considered groundless.12

Pyrrhonist skeptics utilized this problem to argue that because every proposed criterion is either groundless or inconclusive, one should suspend judgment regarding knowledge claims. Ultimately, the problem of the criterion highlights the difficulty of finding an indubitable foundation for human knowledge, forcing philosophers to continuously reexamine their assumptions and the standards they use to define truth.12