In arriving at the relevant ...

In arriving at the relevant theory about the specifics of our faculty of vision we will presumably use our eyes to gather relevant data. Based on such data we come to know about the optic nerve, the structure of our eyes, the rods and cones, etc., so as to explain how it is that vision gives us reliable access to the shapes and colors of objects around us. In reliably arriving at that theory we thus exercise the very faculty whose reliability is explained by the theory. There is no vice in this sort of circularity.
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 Ernest Sosa

Quotes from the same author

When I accept someone's testimony, I am thus only a small part of the full seat of epistemic competence, which might include many others in a long chain. My own contribution might then be slight, just through the perceptual and linguistic competence involved in knowing what someone is saying or writing, etc.
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 Ernest Sosa
It is also certain that when we assent to some piece of reasoning when our perception of it is lacking, then either we go wrong, or, if we do stumble on the truth, it is by accident, so that we cannot be sure that we are not in error.
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 Ernest Sosa
Flourishing is properly the main human end, and flourishing is activity of soul that succeeds in accord with virtue.
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 Ernest Sosa
Since human good is what humans ought to pursue, the pursuit of interest to Aristotle is then such activity of soul, that which constitutes human good, namely activity that attains desiderata, where the attainment is in accord with virtue.
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 Ernest Sosa
It is possible to produce something that is grammatical either by chance or under the supervision of another. To be proficient in grammar, then, one must both produce what is grammatical and produce it grammatically, that is, in accord with knowledge of grammar in oneself.
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 Ernest Sosa