In Metaphysics 4.6, Aristotle summarizes the arguments from his skeptic opponents in this paragraph:
There are, both among those who have these convictions and among those who merely profess these views, some who raise a difficulty by asking, who is to be the judge of the healthy man, and in general who is likely to judge rightly on each class of questions. But such inquiries are like puzzling over the question whether we are now asleep or awake. And all such questions have the same meaning. These people demand that a reason shall be given for everything; for they seek a starting-point, and they seek to get this by demonstration, while it is obvious from their actions that they have no conviction. But their mistake is what we have stated it to be; they seek a reason for things for which no reason can be given; for the starting-point of demonstration is not demonstration.According to Aristotle, when anyone inquires about who is likely to judge rightly on each class of questions, he is seeking to cast doubt on opinions of one’s preferred experts and authorities. If you say that you prefer the beliefs of X to that of Y, the skeptic will undermine the grounds for which you are preferring X. The question is do we accept that we are justified in believing a particular issue only by appealing to some further principle—if such a condition to accepted then nothing can be judged because every principle will need a further justification. Aristotle points out that it is futile to appeal to the authority of any figure—the analysis should begin with what requires proof and what does not, and in case something requires proof, then what kind proof is required.