The word critic comes from the Greek κριτικός (kritikós), "able to discern, which in turn derives from the word κριτής (krités), meaning a person who offers reasoned judgment or analysis, value judgment, interpretation, or observation. The term can be used to describe an adherent of a position disagreeing with or opposing the object of criticism.
Modern critics include professionals or amateurs who regularly judge or interpret performances or other works (such as those of artists, scientists, musicians, or actors), and typically publish their observations, often in periodicals. Critics are numerous in certain fields, including art, music, film, theatre or drama, restaurant, and scientific publication critics.
Criticism is the activity of judgement or informed interpretation and, in many cases, can be synonymous with "analysis." In literary and academic contexts, the term most frequently refers to literary criticism, art criticism, or other such fields, and to scholars' attempts to understand the aesthetic object in depth. In these contexts the term "critic," used without qualification, most frequently refers to a scholar of literature or another art form. In other contexts, the term describes hostility or disagreement with the object of criticism. Sometimes context, and the contentiousness of the subject, are the only differentiating factors between these two approaches. In politics, for instance (as in the phrase "criticism of U.S. foreign policy"), criticism almost exclusively refers to disagreement—while in an academic, artistic, or literary context (as in "criticism of Romantic poetry") it usually refers to the activity of subtle interpretation or analysis.
There can be tension between friendly support and useful criticism. A critic might usefully help an individual artist to recognize what is poor or slapdash in their body of work, but the critic may appear harsh and judgmental in the process. Useful criticism is a practical part of constructive criticism.
An alternative definition of the difference is "Criticism by me is constructive. Criticism of me is destructive." More usefully, whether criticism is constructive or destructive depends heavily on the use the listener makes of it. "Whether the critic meant to be constructive or destructive in pointing out that "2+2 does not equal 7" is not nearly as important as whether the person addressed corrects his arithmetic. Many of the common definitions of "constructive" and "destructive" border on logical fallacies: here the given definition of "constructive" is very close to argument from authority, and the definition of "destructive" makes it easy to fall into argument ad hominem. Criticism cannot be ignored or accepted based on whether it is constructive or destructive.
One of the symptoms of Narcissistic Personality Disorder is an inability to tolerate any forms of criticism.
The critic is also considered to be the psychic inverse of genius. This insight was formulated early by Lessing as "not every critic is a genius, but every genius is born a critic...genius has the proof of all rules within itself." Kant scholar Jane Kneller has read this to indicate that, as opposed to the externally oriented and culturally dependent critic, "genius demonstrates its autonomy not by ignoring all rules, but by deriving the rules from itself.