Perverted by Language:
Grammatical and Linguistic Errors That Drive Us Mad
‘The exception that proves the rule'
Wouldn't it be handy if this expression really meant what most people take it to mean? You make a general statement about something, insisting it to be an unchallengeable rule, and someone thinks of an exception to this rule. Simply by invoking this phrase you can discount their challenge. Wrong. This is no get-out-of-jail-free card. The verb 'proves' is used here in the sense of 'testing', not confirming. It is simply saying that the exception does indeed challenge the rule - not the exact opposite, which is how it's used today.
'It begs the question'
Even the most articulate writers and broadcasters - for whom words are everything - misuse this phrase. Again it is because of a misunderstanding of the meaning of the verb. 'Begs' is here used in its archaic meaning of 'prejudice' so that the phrase actually means 'It assumes the truth of a proposition requiring proof'. Today you never hear it used except - mistakenly - as a completely unnecessary alternative to saying 'it raises the question'.
This is one of those instances in English where a word or phrase has a kind of directional logic to it, as well as deriving from a verb, so that the use of the correct preposition is crucial to the meaning. If you and a friend hold different views on a subject then your views differ from hers. They don't differ to hers. Therefore your views are different from hers, never different to. It's the spatial imagery of separation that demands the word from, unlike its opposite, similar to.
This is even worse, an American import that makes even less sense than 'different to'. 'Than' is a conjunction that introduces a comparison, so it can only be used with an adverb or adjective that is comparative, such as 'bigger than' or 'smaller than'. Saying 'different than' makes as much sense as if you said 'big than' or 'small than'.
'Less' and 'Fewer'
This is another widespread mistake. Both words are comparative adjectives, but 'less' means 'smaller in degree' while 'fewer' means 'smaller in number'. Therefore while one dog may be 'less spotty' than another - smaller in the degree of spottiness - it can only have 'fewer spots' - smaller in the number of spots. Saying it has 'less spots' is as meaningless as saying 'fewer spotty'.