Everyone concedes that taste differs. Yet nobody behaves as though aesthetic judgements were merely reports of preference — we argue about films, defend our judgements with reasons, and think someone who finds a masterpiece worthless has missed something rather than merely differed. Aesthetics begins with that tension and finds it surprisingly hard to resolve.
On beauty, the ancient dispute is whether it resides in the object or the observer. Plato took it to be objective, a Form in which beautiful things participate imperfectly. Hume moved it toward the observer while resisting relativism: beauty exists in the mind that contemplates, but the judgement of qualified critics — those with practice, comparison and freedom from prejudice — converges enough to constitute a standard of taste. Kant's solution was subtler: judgements of beauty are subjective, since they rest on a felt response rather than on concepts, yet we make them with a claim to universal agreement, because the response arises from capacities we share. That is why we say the painting is beautiful rather than that we happen to like it.
The definition of art has proved even more resistant, largely because twentieth-century art set out to break every proposed boundary. Representation fails on abstract work. Expression fails on much conceptual and formalist art. Formalism, which locates art in significant form, struggles with work whose point is its idea rather than its arrangement. Duchamp's readymades made the problem concrete: an ordinary manufactured object, placed in a gallery, functioning as art — with nothing intrinsic distinguishing it from its identical twin in a hardware shop.
That pushed theorists toward the institutional answer: something is art if the relevant artworld confers that status on it. This has the advantage of matching practice and the disadvantage of seeming to make art whatever curators say it is, with no independent standard. Others suggest art is a cluster concept with no necessary conditions — a family resemblance, in Wittgenstein's sense, where members share overlapping features but no single defining one.
A final live question concerns art and morality. Can a work be aesthetically excellent while being morally repugnant? Autonomists say yes: aesthetic value is independent of moral value, and confusing them is a category error. Moralists reply that a work soliciting responses we ought not to have has thereby failed at something internal to it — if a film asks you to enjoy cruelty and you cannot, the failure is aesthetic as well as ethical. The dispute matters well beyond philosophy, since it underlies most public arguments about troubling art and troubling artists.