||Qualia (singular: quale) are those properties of conscious mental states or events that determine 'what it is like' for the subject of those states or events to undergo them. Paradigm examples of qualia include the particular painfulness of some pain state, the sensation of being tickled, the taste of lemon, or the smell of fresh mown grass. Somewhat more contested examples might include 'primary qualities' presented in perception, such as shape or number; emotions such as feelings of elation or a sensation of creeping depression; or qualititive features that may accompany cognition (such as one's 'internal monologue', or the feeling of something being 'on the tip of one's tongue'). Even within the canonical range of qualia the notion is contested, and some argue that we cannot make clear sense of it at all. If it can be made sense of, then a key question is whether qualia are irreducibly nonphysical, or alternatively can be naturalised through reduction to or identification with some physical or functional property. Questions also arise about our knowledge of qualia (our own and others), and about the relationship between qualia and intentional content: qualia have often been thought of as non-intentional features of mental states, although this position has recently been widely challenged.