Question

"There is no mother but loves her child." In this sentence, what type of part of speech is 'but'? Could you please explain your answer?

Answer 1

This 'but' is a pseudo relative pronoun.

Explanation:

Though 'but' is usually a conjunction, 'but' in this sentence is followed by a verb 'love(s)' and works as a pronoun. This can be regarded as a pronoun.

You can replace this 'but' with a relative pronoun and negative word.

`=`There is no mother who does not love her child.

Other example:
"There is no rule but has some exceptions." means that every rule has some exceptions.

See:
https://www.englishgrammar.org/relative-pronouns-2/