The Jesus wrote...
Art, in its purest form, is expression. Regardless of how vulgar, inappropriate, or completely depraved something may be, that doesn't mean that it can't be defined as art. Personally, I try to find some type of deeper meaning in whatever I consider as art, but it doesn't mean that it has to be subtle. A man sodomizing another man with a screwdriver, the actual act not just a painting or some other type of picture, can be considered art in some contexts. If a person finds some significance in the expression of an action, whether it is photographed, painted, sculpted, videotaped, or even performed IRL, no objections can truly deny its artistic credibility.
I guess on the most basic level, art is just an expression of something. It would probably be too complicated to define it as something more specific, and what could be called "art" then.
blind_assassin wrote...
It's a basic urge. Art that is meant solely for intellectual and spiritual enjoyment doesn't exist in societies that don't have the security to allow for economic specialisation and meeting more than basic needs. Hentai is just porn that takes slightly more effort to produce. Actually considering hentai to have any spiritual element on it's own (sex arguably does but that's a different discussion) is either said in jest or by incredibly pretentious people that have very limited horizons.
It's true that art meant solely for those purposes may not exist, but since anyone could do anything they liked and call it art, anything and everything is art, no matter what it might be. If it's captured in some sort of medium, then it can be viewed time and time again, if not, then so be it. Hentai can be enjoyed as just art, just as one can call pornography "art". Porn would have been used some time or another as art to communicate something, and as hentai is porn, we can definitely use it as art. Besides, why can't everything have some sort of meaning, or at least, be able to have a meaning attached to it, no matter how stupid and useless?