Consider the below sentence.
Nothing is as painful as what he went through.
What part of speech does 'nothing' belong to? Traditionally, it is analysed as a pronoun, but I am not too convinced by this analysis: for instance, whereas 'nothing' can be followed by a modifier (as in Thus far he has suggested nothing helpful), pronouns are very limited in both the type and range of modifiers that they allow. The pronoun She in the sentence She was denied access cannot be modified by a pre-head modifier (Young she was denied access is not grammatical), nor can it be modified by a post-head modifier (apart from a relative clause, though She who committed the crime was denied access does sound very archaic).