Problems with explaining English grammar often reside in the terminology. There is often a big assumption that we understand what the terms mean. Simple is, in my opinion, one of the most important examples.
Recently I have noticed two terms, present perfect and present perfect simple.
When I looked up simple in multiple dictionaries it stated that simple meant a verb tense without an auxiliary. So now I'm confused because the perfect tense uses the auxiliary has/had. So now I'm thinking, the meaning is a verb tense without an auxiliary "to be" verb means simple, but I can't find that in writing anywhere. Being that I can't find it written anywhere and that I can find present perfect written without the "simple" term added at the end, I'm starting to think that the present perfect is in fact not simple, but I have no idea.
I think the biggest problem with grammar, is it is somewhat scientific, yet it often lacks citation. People state rules all the time without ever stating the origins of them.
Ideally, I'd like to know who came up with using the term simple in English grammar and what they actually intended that word to mean and why we seem to be using it and NOT using to talk about the present perfect. My research on Google had led to no results on these matters.
Update 5/20/2021 I believe/hope I've found the answer from Collin's Dictionary https://www.collinsdictionary.com/us/dictionary/english/simple
"In grammar, simple tenses are ones which are formed without an auxiliary verb 'be,'"
I have visited America. (present perfect simple) UK grammar.
I have visited America. (present perfect) US grammar.
This seems to be a feature of British grammar, whereas in American grammar this is not followed. There seems to be the idea that any auxiliary verb eliminates the "simple" state (for lack of a better word) of the verb in American grammars, whereas in the UK it is only the "be" verb that eliminates the simple state.
See the term present perfect simple used here: https://learnenglish.britishcouncil.org/grammar/intermediate-to-upper-intermediate/present-perfect
Note the authority of the source.
We use the present perfect simple (have or has + past participle) to talk about past actions or states which are still connected to the present.
See the present perfect used here from a US source: https://owl.purdue.edu/owl/general_writing/grammar/verb_tenses/index.html
I hope this clears things up for a lot of English learners out there.