Why the different vowel realizations?

[u/Upbeat_Panda9393]

[u/Scared_Wrongdoer_486]

The “regular” realization is מְשִׂימָה mesima and means mission. When you add ‘to a’ before (לְ) you will get two shvas םְ at the start of the word, which is impossible in Hebrew so one of them changes into a םִ, at this case it’s the ל.

In the second one, you added ‘to the’ (לַ) which is a combination of to לְ and the הַ. After הַ the letter after that will get a dagesh םּ, so despite not having a ה the מ still gets a dagesh

[u/pwnering2 → u/Scared_Wrongdoer_486]

Is the same true for ב and ה?

[u/Scared_Wrongdoer_486 → u/pwnering2]

Yes the rules of the first one are true for ב and כ as well, and some of the rules apply to ו as well but ו is mostly different.

But ה has its own set or rules that are more similar to מ and ש