Do you think there should be an apostrophe in 'his'? .... Not to mention 'hers', 'ours', 'yours', 'theirs'. .... The words as they are spelled are possessive pronouns and indicate possession without the need for the apostrophe and just happen to end with 's' unlike 'my', 'mine', 'your' or 'her' which obviously do not have an apostrophe.
Thanks. Interesting. I may have learned something here (after goodness knows how many decades of not knowing/realising!) ...
The usual convention is that one indicates possession by adding an "s",
with a preceding apostrophe, to a word (usually a noun).
When it comes to pronouns, I have always accepted that we do not use I's, you's, he's, we's, you's or them's because there are specific possessive pronouns available (my, your (formally thy), his, our, your & their)
which do not simply add an 's' to the corresponding pronoun (hence don't have/need an apostrophe). If these possessives
had (which they haven't) been formed just by addition of a terminal 's', then I probably
would have expected the apostrophe to be included.
[I'm less sure what part of speech are things like "yours", "ours" and "theirs"]
"Her" and "it" seem rather different, in that the accepted corresponding possessives
are formed by simply adding an 's' to the pronoun. For that reason, I think I have probably always believed that both 'ought' to have an apostrophe - although, as I said, I was taught that one should not include an apostrophe in the (possessive) " it's ",
since it then would be confused with the 'contracted " it's " meaning "it is". However, there is no such potential confusion with " her's ", so I think I have probably always included an apostrophe when I have written that.
So, maybe you have educated me, after nearly seven decades of speaking this language
Kind Regards, John