Irrational in the context of Albert Ellis (psychologist)

Rationality is the quality of being guided by or based on reason. In this regard, a person acts rationally if they have a good reason for what they do, or a belief is rational if it is based on strong evidence. This quality can apply to an ability, as in a rational animal, to a psychological process, like reasoning, to mental states, such as beliefs and intentions, or to persons who possess these other forms of rationality. A thing that lacks rationality is either arational, if it is outside the domain of rational evaluation, or irrational, if it belongs to this domain but does not fulfill its standards.

There are many discussions about the essential features shared by all forms, or accounts, of rationality. According to reason-responsiveness accounts, to be rational is to be responsive to reasons. For example, dark clouds are a reason for taking an umbrella, which is why it is rational for an agent to do so in response. An important rival to this approach are coherence-based accounts, which define rationality as internal coherence among the agent's mental states. Many rules of coherence have been suggested in this regard, for example, that one should not hold contradictory beliefs or that one should intend to do something if one believes that one should do it.

The problem of philosophical objectivity is contrasted with personal subjectivity, sometimes exacerbated by the overgeneralization of a hypothesis to the whole. For example, Newton's law of universal gravitation appears to be the norm for the attraction between celestial bodies, but it was later refined and extended—and philosophically superseded—by the more general theory of relativity.

A superstition is any belief or practice considered by non-practitioners to be irrational or supernatural. It is commonly applied to beliefs and practices surrounding luck, fate, magic, amulets, astrology, fortune telling, spirits, and certain paranormal entities, particularly the belief that future events can be foretold by specific unrelated prior events.

The word superstition is also used to refer to a religion not practiced by the majority of a given society regardless of whether the prevailing religion contains alleged superstitions or to all religions by the antireligious.

In the sciences and in historiography, denialism is the rejection of basic facts and concepts that are undisputed, well-supported parts of the scientific consensus or historical record on a subject, in favor of ideas that are radical, controversial, or fabricated. Examples include Holocaust denial, AIDS denialism, and climate change denial. The forms of denialism present the common feature of the person rejecting overwhelming evidence and trying to generate political controversy in attempts to deny the existence of consensus.

In psychology, denialism is a person's choice to deny reality as a way to avoid believing in an uncomfortable truth. Denialism is an essentially irrational human behavior that withholds the validation of a historical experience or event when a person refuses to accept an empirically verifiable reality.

Rational egoism (also called rational selfishness) is the principle that an action is rational if and only if it maximizes one's self-interest. As such, it is considered a normative form of egoism, though historically it has been associated with both positive and normative forms. In its strong form, rational egoism holds that to not pursue one's own interest is unequivocally irrational. Its weaker form, however, holds that while it is rational to pursue self-interest, failing to pursue self-interest is not always irrational.

Originally an element of nihilist philosophy in Russia, it was later popularised in English-speaking countries by Russian-American author Ayn Rand.