When does one pronounce the T in "-ut"?

Question

In but, brut, and chut the t is pronounced. But in lut and fut it isn't. What is the rule for words ending in -ut, if there is one? Is it that it's silent for passé simple verb conjugations, but otherwise pronounced?

Answer 1

There isn't a specific rule for the -ut ending. There are general rules for the pronunciation of endings of conjugated verbs: -e, -t and -s are silent, -ent is silent, -ez is prounced [e]…

A final -t is generally silent. But there is a common phenomenon that the final consonant is often not silent in words of one syllable (net, mat, sud, cap, …). This phenomenon does not apply to conjugated verbs, only to words in their base form. Hence, for example, “Chut !” = “be silent” pronounced [ʃyt], vs. “il chut” = “he fell” pronounced [il.ʃy]; “un lut” [œ̃.ly] vs. “il lut” [il.ly]. But it's just a common phenomenon, not a rule: there are many one-syllable words where the final is silent (pet, rat, nid, …).

See also Quelles sont les lettres qu'on ne prononce pas à la fin d'un mot ? for a more general overview of the pronunciation of final letters.

Historically, all of these final letters were pronounced (and the word might have had more sounds at the end, for example as part of a Latin declension). But French has tended to shave off the end of words, often removing the last consonant as well as the Latin declension. But once again, this is just a common phenomenon, not an absolute rule. Modern spelling tends to add a final -e to indicate that the last consonant is pronounced, and leave off the -e to indicate that the last consonant is etymological. But many one-syllable words have no -e in their spelling even though the last consonant has not become silent. Note that from a historical perspective, the question is not “why is this letter not pronounced” but “why does the spelling not convey the pronunciation” — the pronunciation evolved naturally, whereas the spelling was chosen deliberately based on a compromise between pronunciation and etymology.

For a few words, there is an added complication that the final consonant may be silent or not depending on regional variations, on the context, on individual speakers or even with free variation. For example: vingt, cinq, dix, donc, persil, … The noun but is one of those. Français de nos régions is a good source of information about regional variations, but they don't seem to have researched but.