Desires are states of mind that are expressed by terms like "wanting", "wishing", "longing" or "craving". A great variety of features is commonly associated with desires. They are seen as propositional attitudes towards conceivable states of affairs. They aim to change the world by representing how the world should be, unlike beliefs, which aim to represent how the world actually is. Desires are closely related to agency: they motivate the agent to realize them. For this to be possible, a desire has to be combined with a belief about which action would realize it. Desires present their objects in a favorable light, as something that appears to be good. Their fulfillment is normally experienced as pleasurable in contrast to the negative experience of failing to do so. Conscious desires are usually accompanied by some form of emotional response. While many researchers roughly agree on these general features, there is significant disagreement about how to define desires, i.e. which of these features are essential and which ones are merely accidental. Action-based theories define desires as structures that incline us toward actions. Pleasure-based theories focus on the tendency of desires to cause pleasure when fulfilled. Value-based theories identify desires with attitudes toward values, like judging or having an appearance that something is good.