system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why is there a 'j' sound when you pronounce the word 'module'?

As a native English speaker I'm confused by this.  Why isn't it pronounced 'MAH-due-lo'?  Are there other words like 'modular', 'modulo', etc. that have a j sound?
gpt
It's called diachronic palatalization and it's a common process in development of languages over time. When two sounds are adjacent, the first is transformed over time to some other more "palatal" sound. That means, first the form is /modu/, but then over time it becomes /modju/ ("modyu") and eventually /modʒu/ ("modzhu"). Diachronic means the forms /modu/ and /modju/ are alternatives of the same, not different words with a different meaning, so you'd say they appear at different times (dia-chron) in history.

(Synchronic palatalization would be if /modu/ and /modju/ had different, unrelated meanings; this happens in some languages like Hungarian but not in English. They happen at the same time (syn-chron). East Finnish is funny because it first lost synchronic palatalization but then gained diachronic palatalization.)

All "mechanical" explanations in this thread are wrong, because you don't *have to have* diachronic palatalization. Sometimes the speakers of a language just do it. It's missing from standard Finnish, for example. There are remnants of older diachronic palatalization patterns, calcified in rules like "käte-" vs "käsi", but it's not currently in effect in any context.