From Wikipedia:
http://en.wikipedia.org/wiki/Grammatical_aspect

Aspects of the present tense:
Present simple (not progressive, not perfect): "I eat"
Present progressive (progressive, not perfect): "I am eating"
Present perfect (not progressive, perfect): "I have eaten"
Present perfect progressive (progressive, perfect): "I have been eating"

Aspects of the past tense:
Past simple (not progressive, not perfect): "I ate"
Past progressive (progressive, not perfect): "I was eating"
Past perfect (not progressive, perfect): "I had eaten"
Past perfect progressive (progressive, perfect): "I had been eating"

I fail to see why the Past simple (not progressive, not perfect): "I ate" is, well, not perfect, if the action is certainly completed. Everything else does make sense (to me) though.

It's my understanding that perfective aspect = finished and imperfective = !perfective = unfinished/habitual/progressive/continuous.

Compare "I ate" and "I have eaten" and put them into context of completed or not-completed. Example:

"I ate, but then I was interrupted."

"I have eaten, but then I was interrupted."

You can easily see how the second one doesn't work.

[Zgarbas]

...^ that's not right....(neither sentence in the second post is correct, I mean)

Past simple represents a completed action in the past. Present perfect represents a recently finished action. Of course it's more complicated than that (present perfect is used for unfinished time intervals, emphasis, etc., using certain times and link words require special uses of tenses, and so on. )

I have eaten today = I have already eaten today, there is no need to eat now.
I ate today = stating the fact that you ate, regardless of context.

I have eaten this before = emphasis on the fact that you've eaten something before.
I ate shrimp before = not really correct, though still used. Still, the fact that the action has occurred is not as important as with the present perfect.

I have eaten = right after a meal to emphasize the fact that you are full.
I ate = More matter-of-fact.

And various other nuances and situations, of course.
Also, chronologically
present continuous>present simple>present perfect/present perfect progressive>past simple>past progressive/past perfect>past perfect progressive.

And also, though the past simple is not perfect, it is not imperfect either. The progressive tenses are imperfect. Also, perfect !== perfective. The past perfect is perfect whereas the past simple is perfective ^^'.

I hope we don't get off-topic before I get a satisfactory answer. :/

@ My question is: why is the simple past, i.e., "I came", "I finished" not considered to have/denote perfective aspect if it obviously indicates an action that is finished/completed?

"In linguistics, the perfect ...is a combination of aspect and tense that calls a listener's attention to the consequences, at some time of perspective (time of reference), generated by a prior situation, rather than just to the situation itself."

Past and perfect are not the same thing.

[Zgarbas]

Because the past simple is perfective whereas the past/present perfect is perfect.

Btw, moved topic to the Kohii Lounge as it is not related to Japanese.

Listen to Zgarbas. They smart person.

Zgarbas Wrote:Because the past simple is perfective whereas the past/present perfect is perfect.

Ah, misread.

Thank you guys.

I was familiar with the idea that perfect != perfective. The first being a tense+aspect combo and the last the aspect switch that informs you that the actions is done/not-done.

But, glory to @Zgarbas that made me see that Wiki never said the contrary. ね

Nice timing! I just taught the present perfect today. It's almost absurd how much English emphasizes time when it comes to tense and aspect. Add conditionals, and you can make analytically dense, yet common and grammatically correct sentences like "If I had been feeling better, then I would have gone jogging." Such a sentence must be mental torture for ESL learners.

[Zgarbas]

I always thought English has pretty easy grammar though =/. Even if for the life of me I could never enumerate the if clauses.

(also, I've been wondering about this...since when is the present continuous called present progressive? Has it always been like this or did they reform the term recently? continuous sounds somuch better...)

@Zgarbas Continuous and progressive are two different aspects, most people use both terms to mean the same since English uses the same form to show it anyway.

From Wiki:
Continuous versus progressive
The progressive aspect expresses the dynamic quality of actions that are in progress while the continuous aspect expresses the state of the subject that is continuing the action. For instance, "Tom is reading" can express dynamic activity: "Tom is reading a book" - i.e. right now (progressive aspect), or Tom's current state: "Tom is reading for a degree" - i.e. Tom is a student (continuous aspect). The aspect can often be ambiguous; "Tom is reading Ulysses" may describe his current activity (it's in his hand), or the state of having started, but not yet finished, the book (it's in his bag).

[Zgarbas]

Ahh, English. They just don't know when to stop overtly complicating things with silly terms ^^. Thanks!