Pleasure, like pain, is hard to define adequately, and a fundamental quality of human experience. In some sense, the concept of pleasure is fundamental for, or at least a fundamental factor in, ethical and moral considerations; in what makes life worthwile; and in what happiness would be, though in either of these cases more seems involved than pleasure alone.

The problem is that 'pleasure' is a very general and vague term, that covers various kinds of feelings and states of mind or body, and that comes, for various reasons, with various problems.

Even so, and regardless of the kinds of pleasure and the various problems related to it, the one thing that everybody seems to agree on is that ceteris paribus human beings are attracted by what pleases and try to avoid what pains them: If it were not for the consequences or for the moral or ethical values one holds, human beings would try to do and get what gives pleasure, and try to undo and avoid what gives pain.

1. Kinds of pleasure

It would seem that there are various kinds of pleasure, and that some of these,  and indeed both bodily and mental pleasures - viz. the pleasures of food and sex, and the pleasures of friendship and love - are known to and sometimes experienced by all (adult) human beings.

Other pleasures - music, mathematics, chess, the taste of fried insects, the viewing of horror films - may be less widely shared, or may be incomprehensible to some.

Thus, rather like the eye can see any kind of - two-dimensional - shape, regardless from what has it, the mind and the body can feel pleased or displeased by any kind of - perceived or imagined - cause, and may do so for many kinds of reasons and prior conditioning, learning or needs.

2. Problems of pleasure

There are also various more or less paradoxical or problematical facts related to pleasures of some kinds at least. Here is a rapid summary of some of these problems.

First, there is the fact that some intense pleasures - such as connected with sex or drink or drugs - may be deemed ethically highly reprehensible, even in the mind of the person desiring the pleasure while condemning it morally. In brief general terms, not everything that pleases is good, and not everything that is good is pleasant.

This makes it difficult to use the unqualified term 'pleasure' in ethics and morals.

Second, what pleases and the extent to which it pleases varies a lot with persons and personal circumstances, and has often no clear or obvious relation to what motivates. Also, what pleases is much dependent on one's personal circumstances: A meal for a starving person has completely different felt qualities and pleasures than the very same meal would have for the same person when properly fed.

This extends the previous point, with similar consequences, and a similar point: There are many kinds and causes of what is said to please.

Third, while intense pleasures tend to be strongly appealing (even if ethically disapproved) less intense possibly more subtle or variegated pleasures, like those involved in friendship or even socializing with people, may also be strong motivators.

Thus, there is no simple or single rule that relates the intensity or duration of pleasant experiences to what one should or should not do.

Fourth, some pleasures, such as those produced by addictive drugs, or those generated by a membership in a political party or religious group, may well be dangerous to oneself or others (and so the cues the body gives about its needs and states may not at all be in its own interest).

This extends previous points: That something pleases is in itself often no good clue to anything else, and both bodily and mental pleasures may be quite deceptive about what is good for oneself or others.

Fifth, some really or apparently unpleasant experiences - watching horror-films; the cathartic experiences produced by staged tragedies or books; the sights or sounds judged 'sublime'; the activities of teasing and tickling; acts involved in sado-masochism - are nevertheless by some deemed pleasurable.

This too extends previous points, and adds an additional complication: Everybody seems to derive some kinds of pleasure from experiences which in itself are not pleasurable. One good example, that seems to hold for everyone and that puzzled Aristotle already, is the pleasure people derive from staged tragedies.

Sixth, while many pleasures are undoubtedly related to states or experiences of the body, others are presumably mostly or only due to states of mind (love, self-respect, jokes, wit) - though it is a bit difficult to see how one could feel a mental pleasure if one has no body, or if one's body is completelely anesthesized.

This again is an example of the many kinds and causes of what is said to please. Incidentally - and also somewhat puzzling - it still seems to be the case that any pleasure is a bodily state. What makes a pleasure mental (a joke, say) rather than physical (a taste in the mouth, for example) is its starting point; what makes a pleasure felt is some bodily state of a living creature.

Seventh, it is an interesting fact about pleasure and all other feelings that they are subjective and personal; that they cannot be shared except imaginatively; and that often they must be inferred from bodily acts and words (both of which may deceive, intentionally or not).

This is another interesting aspect, especially in an epistemological sense: While feelings are of fundamental human importance, their status as merely subjective facts related to the mental and bodily states of a person, that are basically private to himself, and can be merely inferred by others on the basis of analogies and behavior, differs a lot from intersubjectively given things.

Eighth, it would seem that pleasure is what makes life seem worthwile to many, while it seems that the capacity for pleasure and pain, and feelings in general, seems to be one basic distinction between computers and machines on the one hand, and living and human beings on the other hand: All animals, at least, except perhaps very simple ones, seem to feel and to have states of pleasure and pain, related to the satisfaction or dissatisfaction of their bodily needs.

Thus, it seems that it are feelings of various kinds that make living things different from machines: Machines and men and animals can calculate and reason (at least to the extent that reasoning can be seen or explained as a kind of calculating), but only men and animals and not machines can feel.