In science

Science

Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...

 and philosophy

Philosophy

Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

, an ad hoc hypothesis is a hypothesis

Hypothesis

A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...

 added to a theory

Theory

The English word theory was derived from a technical term in Ancient Greek philosophy. The word theoria, , meant "a looking at, viewing, beholding", and referring to contemplation or speculation, as opposed to action...

 in order to save it from being falsified. Ad hoc hypothesizing is compensating for anomalies not anticipated by the theory in its unmodified form.

In the scientific community

Scientists are often skeptical

Scientific skepticism

Scientific skepticism is the practice of questioning the veracity of claims lacking empirical evidence or reproducibility, as part of a methodological norm pursuing "the extension of certified knowledge". For example, Robert K...

 of theories that rely on frequent, unsupported adjustments to sustain them. This is because, if a theorist so chooses, there is no limit to the number of ad hoc hypotheses that they could add. Thus the theory becomes more and more complex, but is never falsified. This is often at a cost to the theory's predictive power

Predictive power

The predictive power of a scientific theory refers to its ability to generate testable predictions. Theories with strong predictive power are highly valued, because the predictions can often encourage the falsification of the theory...

, however. Ad hoc hypotheses are often characteristic of pseudoscientific subjects.

Note that an ad hoc hypothesis is not necessarily incorrect; in some cases, a minor change to a theory was all that was necessary. For example, Albert Einstein

Albert Einstein

Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...

's addition of the cosmological constant

Cosmological constant

In physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe...

 to general relativity

General relativity

General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...

 in order to allow a static universe

Static universe

A static universe, also referred to as a "stationary" or "Einstein" universe, is a model in which space is neither expanding nor contracting. Albert Einstein proposed such a model as his preferred cosmology in 1917...

 was ad hoc. Although he later referred to it as his "greatest blunder", it may correspond to theories of dark energy

Dark energy

In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...

.

Naturally, some gaps in knowledge, and even falsifying observations must be temporarily tolerated while research continues. To temper ad hoc hypothesizing in science, common practice includes falsificationism (somewhat in the philosophy of Occam's razor

Occam's razor

Occam's razor, also known as Ockham's razor, and sometimes expressed in Latin as lex parsimoniae , is a principle that generally recommends from among competing hypotheses selecting the one that makes the fewest new assumptions.-Overview:The principle is often summarized as "simpler explanations...

). Falsificationism means scientists become more likely to reject a theory as it becomes increasingly burdened by ignored falsifying observations and ad hoc hypotheses.