Abilities are powers an agent has to perform various actions. They include common abilities, like walking, and rare abilities, like performing a double backflip. Abilities are intelligent powers: they are guided by the person's intention and executing them successfully results in an action, which is not true for all types of powers. They are closely related to but not identical with various other concepts, such as disposition, know-how, aptitude, talent, potential, and skill.

Theories of ability aim to articulate the nature of abilities. Traditionally, the conditional analysis has been the most popular approach. According to it, having an ability means one would perform the action in question if one tried to do so. On this view, Michael Phelps has the ability to swim 200 meters in under 2 minutes because he would do so if he tried to. This approach has been criticized in various ways. Some counterexamples involve cases in which the agent is physically able to do something but unable to try, due to a strong aversion. In order to avoid these and other counterexamples, various alternative approaches have been suggested. Modal theories of ability, for example, focus on what is possible for the agent to do. Other suggestions include defining abilities in terms of dispositions and potentials.

An important distinction among abilities is between general abilities and specific abilities. General abilities are abilities possessed by an agent independent of their situation while specific abilities concern what an agent can do in a specific situation. So while an expert piano player always has the general ability to play various piano pieces, they lack the corresponding specific ability in a situation where no piano is present. Another distinction concerns the question of whether successfully performing an action by accident counts as having the corresponding ability. In this sense, an amateur hacker may have the effective ability to hack his boss's email account, because they may be lucky and guess the password correctly, but not the corresponding transparent ability, since they are unable to reliably do so.

The concept of abilities and how they are to be understood is relevant for various related fields. Free will, for example, is often understood as the ability to do otherwise. The debate between compatibilism and incompatibilism concerns the question whether this ability can exist in a world governed by deterministic laws of nature. Autonomy is a closely related concept, which can be defined as the ability of individual or collective agents to govern themselves. Whether an agent has the ability to perform a certain action is important for whether they have a moral obligation to perform this action. If they possess it, they may be morally responsible for performing it or for failing to do so. Like in the free will debate, it is also relevant whether they had the ability to do otherwise. A prominent theory of concepts and concept possession understands these terms in relation to abilities. According to it, it is required that the agent possess both the ability to discriminate between positive and negative cases and the ability to draw inferences to related concepts.

Abilities are powers an agent has to perform various actions. Some abilities are very common among human agents, like the ability to walk or to speak. Other abilities are only possessed by a few, such as the ability to perform a double backflip or to prove Gödel's incompleteness theorem. While all abilities are powers, the converse is not true, i.e. there are some powers that are not abilities. This is the case, for example, for powers that are not possessed by agents, like the power of salt to dissolve in water. But some powers possessed by agents do not constitute abilities either. For example, the power to understand French is not an ability in this sense since it does not involve an action, in contrast to the ability to speak French. This distinction depends on the difference between actions and non-actions. Actions are usually defined as events that an agent performs for a purpose and that are guided by the person's intention, in contrast to mere behavior, like involuntary reflexes. In this sense, abilities can be seen as intelligent powers.

Various terms within the semantic field of the term "ability" are sometimes used as synonyms but have slightly different connotations. Dispositions, for example, are often equated with powers and differ from abilities in the sense that they are not necessarily linked to agents and actions. Abilities are closely related to know-how, as a form of practical knowledge on how to accomplish something. But it has been argued that these two terms may not be identical since know-how belongs more to the side of knowledge of how to do something and less to the power to actually do it. The terms "aptitude" and "talent" usually refer to outstanding inborn abilities. They are often used to express that a certain set of abilities can be acquired when properly used or trained. Abilities acquired through learning are frequently referred to as skills. The term "disability" is usually used for a long-term absence of a general human ability that significantly impairs what activities one can engage in and how one can interact with the world. In this sense, not any lack of an ability constitutes a disability. The more direct antonym of "ability" is "inability" instead.

Various theories of the essential features of abilities have been proposed. The conditional analysis is the traditionally dominant approach. It defines abilities in terms of what one would do if one had the volition to do so. For modal theories of ability, by contrast, having an ability means that the agent has the possibility to execute the corresponding action. Other approaches include defining abilities in terms of dispositions and potentials. While all the concepts used in these different approaches are closely related, they have slightly different connotations, which often become relevant for avoiding various counterexamples.

The conditional analysis of ability is the traditionally dominant approach. It is often traced back to David Hume and defines abilities in terms of what one would do if one wanted to, tried to or had the volition to do so. It is articulated in the form of a conditional expression, for example, as "S has the ability to A iff S would A if S tried to A". On this view, Michael Phelps has the ability to swim 200 meters in under 2 minutes because he would do so if he tried to. The average person, on the other hand, lacks this ability because they would fail if they tried. Similar versions talk of having a volition instead of trying. This view can distinguish between the ability to do something and the possibility that one does something: only having the ability implies that the agent can make something happen according to their will. This definition of ability is closely related to Hume's definition of liberty as "a power of acting or not acting, according to the determinations of the will". But it is often argued that this is different from having a free will in the sense of the capacity of choosing between different courses of action.