As a conjunction, it connects two ideas that contrast, like 'I was tired, but I kept going.' As a preposition, it can mean 'except,' as in 'everyone but me.'
From Old English 'butan' meaning 'without, outside, except.' It developed from a combination of 'be-' (by) and 'utan' (out). Over centuries, its use narrowed into the contrast and exception meanings we use today.
This tiny word is a master of drama: it tells your brain, 'Pay attention, something different is coming.' In conversations, whatever comes after 'but' usually feels more important than what came before. That’s why in persuasion or arguments, people listen most carefully to the clause after 'but.'
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