The conjunction “but” often means “and”

The words and and but are coordinating conjunctions. Whereas and is typically symmetric (the phrases before and after and can be interchanged without changing meaning), but is asymmetric. The word but is used to coordinate or subordinate a clause of concession or exception. However, but is also used in a way that implies an and connection [1]:

Let me begin with a mantra of 20th-century math education: “ ‘but’ means ‘and’.” We all know that this makes partial sense: namely, if one says “John is poor but happy” one is asserting both “John is poor” and “John is happy”. Nevertheless “but” is a major component in the structure of thought (like “nevertheless”), and the version having “but” as the connective is not the same as the conjunction of the two simple assertions. Many English speakers would find “John is poor but happy” cogent but not “John is rich but happy”. You will easily find more and subtler everyday examples. Examples within mathematics are subtler, inexhaustible, but [!] more elusive; […]

Even when but takes on the meaning of and, but stays syntactically asymmetric.

Keywords: natural language, coordinators, mathematics, logic, reasoning, precision

Reference
[1] Chandler David: The Role of the Untrue in Mathematics. The Mathematical Intelligencer Summer 2009, Volume 31, Number 3, pp. 4-8.