I often find myself to be impatient, often frustrated, when people claim something to be 'obvious', and never more than when I think that they are using it incorrectly. An example of this might be "obviously, Hitler was an evil man", or "obviously, it's better to be poor and happy than rich and sad" - this is because I wish justification for their claim, and do not want to simply accept it (in these cases because of popular opinion). I realise that both of these examples are ethical, but is there anything that is understood by philosophers to be obvious (and by obvious I mean without need of qualification or justification)?
If I may reply in terms of personal experience: when students start"doing philosophy", one of the first thing they (need to) learn isthat what seems obvious to x may be much less so to y. As soon as things become interesting, they stop being obvious. Yet I have noticed that this is not the only important lesson about "obvious". For once they have understood therelativity of "obviousness" then they also need to realize that no answer in terms of “obviously p ” will ever convince anyonewho was not already convinced that p in the first place. Philosophy is not doneadverbially, as it were, since “obviously (clearly, truly, certainly…) 2 + 2 =4” is no more (nor less) convincing that “2 + 2 = 4” as a reply to someone whoshare a different sense of the obvious. So there are no obvious p on which philosophers agree (or they would not discuss them) and no obvious way (i.e. "obviously") to tackle them.