I have a basic grammar question about the past tense. If I met a guy yesterday, which tense should I use about his name today?
"Yesterday I met a guy, his name is/was John."
Either is possible. In my personal opinion it comes down to context. Was this a fleeting acquaintance or someone you are likely to take up with in the future?
I met this guy yesterday, his name was John. He was very rude - I hope I never meet him again!
I met this guy yesterday, his name is John. We're going to meet up for coffee. Come along and I'll introduce you.
You can see in my examples that, in the first case, you are leaving John 'in the past'. In the second you are continuing the relationship to the present and into the future.
I'll be interested to see if others agree with me.
From a purely logical standpoint, only "was" is strictly correct, because you can't actually know whether he's changed his name since you met him. Very unlikely, but it's possible! You can say for sure what his (stated) name was at the time you met him, but you cannot know for sure what his name is at the present (without meeting or communicating with him again).
I'm splitting hairs here, of course. In common usage, both are equally acceptable. As @chaslyfromUK answered, the preferred choice is context-dependent.
EDIT (after reviewing all the comments): I'm coming back to this after a bit of a hiatus, and the discussion has really grown. :) As I said, the more appropriate tense is really context-dependent, even in the circumstance of meeting someone, which is what the question was all about. Contrast these two sentences: "I happened upon a homeless stranger yesterday and exchanged a few words. His name is/was John" and "I made a new friend yesterday. His name is/was John". Now which would you pick in each of those sentences?
I think most would agree that was sounds better in the first case, while is sounds better in the second.Despite using "was" in the first case, there is no implication that the homeless stranger is likely to have changed his name in the course of a day, which would be highly improbable. Rather, the implication is that the meeting was a one-off event, unlikely to be repeated, so the memory of the meeting is in the past. In contrast, the second case signifies a relationship that is likely to be ongoing and current, so "is" works better.
I'm sorry if I gave the impression that I felt was was linguistically more appropriate from my first line. I'm not editing it, so that people can see what the contretemps in the comments was all about. But I felt that the qualifier ("I'm splitting hairs") in the paragraph immediately following it would have made my actual opinion quite clear. The point is this: language is often no respecter of logical precision. Sometimes, the choice that "sounds better" wins out over something that would actually be more logically correct.
The general answer is probably that this is a context-specific consideration. In this example
was may be probably preferable, since
is (to my ear at least) imposes a bit of a tense-clash. But if we're talking about something more permanent and immutable then
is might be preferable: e.g.
"Yesterday the Sun emitted a flare. The Sun was Earth's nearest star"
.. both sounds daft and adds a degree of ambiguity by suggesting (again due to the context) that this is no longer the case. This is obviously absurd, but there may be other cases where the ambiguity causes genuine confusion.