A concept in Russian is really confusing me, that is, when a verb, such as Быть requires the use of (Instrumental), does this mean that you CAN NOT use another case with this verb?
Are there verbs which can be used with different cases, and this changes the semantic meaning?
And for any verb + noun,adjective, etc. Is the prepositional case always an option, because one can always throw in a На, О, В after the verb?
Let me give an example: One of the meanings given to the verb Находить: Come (over На+Acc case): Could anyone provide me an example where this would apply? I am not sure what the dictionary means here.
In short, Verbs govern cases, but when, where, how, and why? Are these case governments OPTIONIAL?