You never return my phone calls how to write this assertive and non assertive

Examples of assertive words include "some, once, already, somebody, something, sometimes, somewhere, someone."

The source also explains that non-assertive words are used " in questions and negatives. They are also used in if-clauses and with adverbs, adjectives, verbs, prepositions and determiners that have a negative meaning."

Examples of non-assertive words include "any, anything, anybody, ever, & yet."

However, as I read the source, I wasn't able to determine exactly what the semantic or pragmatic difference between assertive and non-assertive words is. I'm hoping that someone can spell this out for me, and/or recommend a source that explains the difference.