Radical skepticism
"It is the view that we know very little. In particular we know very little, if anything, about a world that is external [ɛksˈtɜːnl] to us."
Skeptical hypotheses
"Radical skepticism makes use of skeptical hypotheses [haɪˈpɒθɪsiːz] (гипотезы, допущения, учение). So these are scenarios [sɪˈnɑːrɪəʊz] which are indistinguishable from normal life, but where one is radically in error. One of these scenarios is the brain-in-a-vat hypothesis [haɪˈpɒθɪsɪs] which is the scenario that one is not causally [ˈkɔːzəli] (каузально) interacting with an environment [ɪnˈvaɪərənmənt] in the usual sort of way that one thinks one is, but rather, one's brain has been taken out of one's head and is floating somewhere in a vat of nutrients [ˈnjuːtrɪənts] (питательные вещества), being fed fake experiences."
The problem of radical skepticism
"As skeptical hypotheses are indistinguishable from normal life, it seems there's no way for us to know that they're false [fɔːls], no way that we could rule them out. And from that conclusion the skeptic seems able to motivate [ˈməʊtɪveɪt] the thought that, well, we don't know anything then, very much, about the world around us."
What the skeptic is trying to do?
"The skeptic [ˈskɛptɪk] does not say that you are a brain in a vat. That's not part of the setup to (выдвижения) a skeptical argument. The skeptic simply says that you have no reason for thinking you're not a brain in a vat. So you can't know that you're not a brain in the vat. The skeptic just says: well, how do you know you are not in those circumstances [ˈsɜːkəmstənsɪz]?
The skeptic tries to get you to see that there's a fundamental tension[ˈtɛnʃən] (напряжённость) in your own concepts. Really, the problem of skepticism relates to the fact that we have some fundamental commitments (обязательства) in epistemology which are inconsistent (несовместимый) with each other."
SOURCES
'Introduction to Philosophy' course (the University of Edinburgh)
https://www.coursera.org/learn/philosophy