I am pretty confused by verb conjugation. I thought that it is not always necessary to add an ending to a verb, which already has it's stem and tense. I thought that it is just necessary to add the subject-suffix if the subject will not be mentioned anywhere else in the sentence.
For example "nai hiruvalye valimar!" and "nai elye hiruva!". "You" is the subject. It is either a suffix (-lye) or a word (elye), but it does not appear as both, like in the theoretical sentence "nai elye hiruvalye!". If that sentence was allowed, I could also create rubbish like "nai elye hiruvalyes valimar!" or "Yé! utúvienyes Tuima!"
Apparently such seemingly redundant tautologies can indeed appear in Quenya, like in "esse úpa nas." That sentence confuses me, for I would either say "esse ná úpa." or "nás úpa." (to say nothing of the weird usage of "he". Why esse, why not erye?)
The outcome of this is the question: Is it just allowed or even obligatory to use the subject as both, word and suffix?
Secondly: There are examples and counterexamples. How can they coexist? Of course one answer might be that the use or double use of the subject is optional. Might there be other reasons? Maybe the subject must be mentioned in the verb (no matter whether it is later mentioned again or not), but this rule can be broken in poetic language?
PS. At times I thought that the verb only needs the pronoun-suffix when there is either no other subject (as a word) or when the other subject is a noun and not a pronoun. Apparently that is wrong for esse is a pronoun (at least in this context) and the verb still has it's suffix.