Etymological fallacy

The etymological fallacy is a genetic fallacy that holds, erroneously, that the historical meaning of a word or phrase is necessarily similar to its actual present-day meaning. This is a linguistic misconception, mistakenly identifying a word's current semantic field with its etymology. An argument only constitutes an etymological fallacy if it makes a claim about the present meaning of a word based exclusively on its etymology, thus distinguishing an alleged "true" (etymological) meaning from the workaday use.

A variant of the etymological fallacy involves looking for the "true" meaning of words by delving into their etymologies. A similar concept are false friends.

Prerequisites
An etymological fallacy becomes possible when a word has changed its meaning over time. Such changes can include a shift in scope (narrowing or widening of meanings) or of connotation (amelioration or pejoration). In some cases, meanings can also shift completely, so that the etymological meaning has no evident connection to the current meaning.

For example:
 * The word hound originally simply meant "dog" in general. This usage is now archaic or poetic only, and hound now almost exclusively refers to dogs bred for the chase in particular.
 * The meaning of a word may change to connote higher status, as when knight, originally "servant" like German Knecht, came to mean "military knight" and subsequently "someone of high rank".
 * Conversely, the word knave originally meant "boy" and only gradually acquired its meaning of "person of low, despicable character".
 * The word lady derives from Old English hlæf-dige ("loaf-digger; kneader of bread"), and lord from hlafweard ("loaf-ward; ensurer, provider of bread"). No connection with bread is retained in the current meaning of either word.

Examples
Not every change in meaning provokes an etymological fallacy; but such changes are frequently the basis of inaccurate arguments.
 * From the fact that logos is Greek for "word", Stuart Chase concluded in his book The Tyranny of Words that logic was mere manipulation of words.
 * Some dictionaries of old languages do not distinguish glosses (meanings) from etymologies, as when Old English geþofta is defined as "one who sits on the same rowing bench; companion". Here the only attested meaning is the second one, while the first is simply the word's etymology.
 * Usage of the word gyp "cheat" has been described as being politically incorrect because it is probably derived from Gypsy.
 * Phrases like to grow smaller or to climb down have been criticised for being incoherent, based on the "true" meanings of grow and climb.

Pitfalls
While the assumption that a word may still be used etymologically can be fallacious, the conclusion from such reasoning is not necessarily false. Some words can retain their meaning for many centuries, with extreme cases like mouse, which denoted the same animal in the Proto-Indo-European language several thousand years ago (as ). Claiming "Your use of the word X is based on an etymological fallacy, therefore the use is wrong" constitutes an argument from fallacy.

Consequently, etymological arguments do not answer the question when a word should be considered having changed in meaning, when a new meaning is a misuse, when an old meaning becomes archaic, and similar. Such problems are complex and are treated in the field of lexical semantics.