I am collecting examples of infinite regress arguments in philosophy. See the category Infinite Regress Arguments. Here is one that is suggested by section 239 of Wittgenstein's Philosophical Investigations. When I hear the word 'red,' how do I know which color is being referred to? The following answer might be given: 'Red' refers to the color of the mental image that hearing the word elicits. But then the question arises once again: How do I know that the color of the mental image is the color to which 'red' refers? Do I need a criterion for that as well? If I do, then I am embarked upon an infinite regress, one that is vicious.
Why is it vicious? Most of us know which color 'red' refers to. But how do we know it? To ask how we know this is to request an epistemological (and therefore a philosophical) explanation. But if the explanation is that 'red' refers to the color of the mental image that hearing the word elicits, then, although we have answered the initial question, we have answered it in a way that allows the posing of a second question of the same form as the first. And so on.