Pseudoscience consists of claims, beliefs, or practices presented as being plausible scientifically, but which are not justifiable by the scientific method. A topic, practice, or body of knowledge can reasonably be considered pseudoscientific when it is presented as consistent with the norms of scientific research, but it demonstrably fails to meet these norms.
Pseudoscience is often characterized by the following: contradictory, exaggerated or unprovable claims; reliance on confirmation bias rather than rigorous attempts at refutation; lack of openness to evaluation by other experts; and absence of systematic practices when developing theories. The term pseudoscience is often considered pejorative because it suggests something is being presented as science inaccurately or even deceptively. Accordingly, those termed as practicing or advocating pseudoscience often dispute the characterization.
The demarcation between science and pseudoscience has philosophical and scientific implications. Differentiating science from pseudoscience has practical implications in the case of health care, expert testimony, environmental policies, and science education. Distinguishing scientific facts and theories from pseudoscientific beliefs such as those found in astrology, alchemy, medical quackery, occult beliefs, and creation science combined with scientific concepts, is part of science education and scientific literacy.
The word "pseudoscience" is derived from the Greek root pseudo meaning false and the English word science, which is itself derived from the Latin word "scientia", meaning "knowledge". Although the term has been in use since at least the late 18th century (e.g. used during 1796 by James Pettit Andrew in reference to alchemy) the concept of pseudoscience as distinct from real or proper science seems to have become more widespread during the mid-19th century. Among the first recorded uses of the word "pseudo-science" was during 1844 in the Northern Journal of Medicine, I 387: "That opposite kind of innovation which pronounces what has been recognized as a branch of science, to have been a pseudo-science, composed merely of so-called facts, connected together by misapprehensions under the disguise of principles". An earlier recorded use of the term was during 1843 by the French physiologist François Magendie. During the 20th century, the word was used as a pejorative to describe explanations of phenomena which were claimed to be scientific, but which were not in fact supported by reliable experimental evidence. From time to time, though, the usage of the word occurred in a more formal, technical manner around a perceived threat to individual and institutional security in a social and cultural setting.