Justification is a basic component of reasoning because it provides us with the warrant which should ground the acceptability of the whole argument. Indeed, justifying an argument consists in providing some principle which is seen as reasonable. In t his perspective, the set of possible justifications may be regarded as the set of those commonplaces that are admitted by a human community and are grounded on the values that are commonly endorsed by the community. I will try to show how (...) the lack of dis cussion about those values that are regarded as obvious may lead to paradoxical conclusions. (shrink)