Your question actually boils down to this: What’s the correct sequence of tenses to use in a complex sentence? As we know, a complex sentence consists of an independent clause using one verb and a dependent or subordinate clause using another verb. In Sentence 1 above, in particular, the independent clause is “I will call you” using the simple future tense verb “will call” and the dependent clause is “after I finish my homework” using the present tense verb “finish.” In Sentence 2, the independent clause is the same as in Sentence 1 but the dependent clause now uses the present perfect tense verb “have finished.”
Are there are any differences in meaning between the two sentences?
My answer is that they actually differ not only in nuance but also in sense. By using the present tense “finish” in Sentence 1, “After I finish my homework, I will call you,” the speaker conveys the idea that finishing the homework would be a short-time action that will be over not long after the time of speaking, as the action “stops” in, say, “After the clock stops ticking, I will call you.” On the other hand, by using the present perfect “have finished” in Sentence 2, “After I have finished my homework, I will call you,” the speaker conveys the idea that finishing the homework would be an extended action that will be completed long after the time speaking, as in, say, the action “have read” in the sentence “After I have read Tolstoy’s War and Peace, I will call you.” In short, in complex sentence constructions, the yardstick for choosing the tense for the verb in the subordinate clause is the expected duration of the action.
The other major determinant for the tense of verbs in a complex sentence is, of course, the logic of the statement itself, which will depend on logical language operators like the adverbs “after” and “unless” and the adverbial phrases “as soon as.” Recall that these adverbs and adverbial phrases function as subordinating conjunctions in complex sentences, providing both link and logic to the main clause and subordinate clause.
Now let’s see what happens when we replace “after” in Sentence 1 and Sentence 2 with some of the adverbs and adverbial phrases you listed above: (1a) “When I finish my homework, I will call you.” (1b) “When I have finished my homework, I will call you.” (2a) “As soon as I finish my homework, I will call you.” (2) “As soon as I have finished my homework, I will call you.” (3a) “Once I finish my homework, I will call you.” (3b) “Once I have finished my homework, I will call you.”
They all make sense, but it should be clear by now that there’s no way of knowing whether it’s the present perfect or the simple present tense that’s more commonly used in such complex sentences. No matter what adverb or adverbial phrase introduces the subordinate clause, it’s the sense or nuance that the speaker wants to convey that ultimately determines the sequence of tenses to be used.
