I think the phrasing is inherently ambiguous and there is no one right answer to the poll. That said, I voted 2016 since that’s what my mind went to. But in real life, if it mattered, I would have sought clarification.
When was last night? 2 days ago? No.
Agreed.
I use “this past” and “this coming” most of the time.
From the perspective of Dec 2017:
“I went to the Bahamas last summer.” - 2017
“I am going to the Bahamas this summer.” - 2018
From the perspective of June 2017:
“I went to the Bahamas last summer.” - 2016
“I am going to the Bahamas this summer.” - 2017
“Last summer” was the most recent complete summer. It has to be finished. Otherwise, it’s “this summer”.
I agree with this. “Last summer” would make me think 2016.
So in October 2017, your would refer to the summer of 2017 as “last summer”?
I answered the poll too quickly. As of today, 2017 is “this past summer” and 2016 is “last summer”.
When was the last breakfast you ate? Yesterday? No, it was this morning. Sure, if you didn’t eat breakfast this morning your answer will be different, but if you did, it doesn’t matter how long ago you ate breakfast prior to today, the last breakfast you ate was this morning and not some earlier date.
Now I wouldn’t make a big deal out of this. Some people think for some reason that last summer was in 2016. They are free to hold that opinion. They’re just wrong, that’s all.
ISTM the most logical interpretation of “last” is “previous”. “Last night” is the previous night, “last month” currently means November, and “last summer” currently means the summer that ended last September, 2017. “Last year” of course was 2016, but that just follows the same logic of “previous” and has nothing to do with the meaning of those other things.
Of course the language has no end of quirks, about which, as I have often said, I could care less, or my head would literally explode. 
So “last summer” means whatever the majority of native English speakers want it to mean, but I’m pretty sure the majority would mean what I just described.
I’ll give you the answer next summer.
For me, I think the difference might be that this month is the month we’re in and last month was the previous month. But we’re not in a summer (at least in the US), so “this summer” does not have an obvious meaning for me. Same with “this Wednesday” (though I would never EVER refer to today as “this [dayoftheweek].” Today is NOT “this Thursday.”) If you can be between the time, like you can be between summers or between Wednesdays, determining when to say “this” or “last” or “next” feels harder. That’s why I use “this past” and “this coming” to be clear when it might not be clear from context. At work, I try to include dates to be clearest.
Wow! The right answer on the first response, and it only took 10 minutes. It even includes the extra info about the summer from the current year being “this past summer.” Which only makes sense since the summer from last year is last summer and the summer from next year is next summer.
You’re right that “this summer” is a bit vague if one is not actually in summer, but I don’t see that as being relevant. To me “this past summer” is semantically identical to “last summer”.
No, the wrong answer on the first response, and the right answer provided in the current 73% to 26% polling result. As noted, “this past summer” is not “extra information”, it means exactly the same thing as “last summer”. Any other interpretation makes no sense and neither does your last sentence. At this point in time, winter 2017, the next summer we are about to have is, obviously, “next summer”. The fact that it won’t happen until the calendar year changes is totally irrelevant. It’s the next one, period. In the same way, the last summer we experienced is, obviously, “last summer”. Whether it happened on the same calendar year we’re currently in is totally irrelevant. It was the last one, period. It’s all about the immediately prior summer and the immediate future one. It has nothing to do with years.
It’s relevant to how I think about the question and why certain examples seem to cut one way for me, while others cut another way.
Since we’re in late fall, about to head into winter here in a few days, “last summer” was this year, 2017.
So when was last November?
What if it’s Saturday at 11:30 pm and I’m calling you from a different time zone?
That is where you are wrong again. The calendar year is completely relevant as while we are in winter of 2017, “next summer” is the summer of 2018. Once we are in the spring of 2018, however, it becomes “this coming summer,” and “next summer” is the one that happens in 2019.
Exactly this.
I was not, but I appreciate the irony. :smack:
Well, whichever it was, I’ve got an alibi.