Standard English expects the present perfect tense to be always used whenever the adverb of time, today, is used.
Have you seen Aunt Sarah today?
Yes, I have seen Aunt Sarah today.
Although the examiners at the Cambridge Exam would applaud one’s blanket usage thereof, I should employ my hands upon a different task, dipping them first into the glue, thence the glass.
Although myself a trifle to the right on the Descriptivist/Purist scale, I nevertheless call the case of limpeting on to this usage of the present perfect, as one does the ship’s mast before the final plunge, a load of the shoddiest. Tenses should be used discriminately, to denote time and one’s passage through it. Rules should not simply exist.
It might insult the sensitive reader to hazard forth that the simple past tense denotes events that occurred in only the past, whilst the present perfect denotes those that have occurred in both the past and at present. Past this, I ask, then: does today happen before, now, or after?
Let us examine again the case of Aunt Sarah. The general idea is that today is not over. You just might see Aunt Sarah in the same collection of 24-hours that have been allotted the title; therefore, you have seen Aunt Sarah.
With this, I agree. This present perfect usage is paramount, whenever, for example, one works with Aunt Sarah in the same building and seeing her again is merely the work of one’s pivoting around the next corner, or one lives in the general area as Aunt Sarah, and she’s known to stop by with baked goods or bad news, or she’s prone to spontaneous FaceTime calls on the same day that you have already seen her, or oneself is a known serial visitor of Aunt Sarah. I take issue, however, with the fact that, if you ever saw Aunt Sarah, then you are mistaken.
A dismissal of the simple past tense’s “I saw Aunt Sarah today” as purely an American vulgarism smacks of the worst kind of linguistic injustice. And, indeed, it is regarded as something of a singularly American sin to say, I saw Aunt Sarah today.
It would be correct, however, to say: I saw Aunt Sarah earlier today, for it uses earlier to denote a time that happened before and will never again occur, so the simple past tense it approved.
Firstly, about this, I should state the obvious: In the sentence, I saw Aunt Sarah today, the earlier is simply omitted and therefore implied; we are intelligently implying that some part of today ended, never to return, or that a particular event or function is now history. In this case, stating earlier would also be something tantamount to a redundancy. And, aside from within the plays of Shakespeare, redundancy is given the stink-eye.
I wrote an article today.
I have written an article today.
I wrote the article, and I am no longer writing the article, thus the action of my writing the article exists solely in the past—but it all happened today. Additionally, I wrote the article during the the morning, a bit in the afternoon, and knitted the loose ends together during the evening. Am I simply to say, then, that I wrote the article earlier? When was earlier? Well, in bits throughout the day. Which day? Today? Yes. Surely, I could rewrite the article later that same day; I could edit the article, too. I could even, though my Sloth prevents it, write another article. However, I can never write that same article again today. The article, as both an idea and artifact, is complete. I cannot link the completed artifact to any present action; therefore, it’s simply in the past.
Let us return to Aunt Sarah, whom I have seen today—only.
Oh, yes? Although Aunt Sarah was viewed by Yours Humbly in the later forenoon through to the early afternoon, lives three hours away by car, hasn’t a computer, smart phone, car of her own, or nearby train-line, enjoys a healthy dose of agoraphobia, is not prone to kidnappings, has an aortic embolism, lost her voice to a pleasant life of Pall Malls, and doesn’t have any legs? It would be for my money that I saw Aunt Sarah today. Need I say earlier? Is that not obvious? More often than not, a common day on Earth begins with the sun’s rising, its staying overhead for some amount of time, and its setting. Moreover, humanity has added things such as seconds, minutes, even hours therein. To complicate things even further, we’ve given names to certain clusters of hours; there’s breakfast, second-breakfast, elevenses, lunch, dinner, supper. You know about those, don’t you?
I sympathize towards rules. I am, however, sympathetic towards rules that exist only due to their making sense; I believe that the smudge in the painting should be intentional. We have an s at the end of nouns to show the plural, we have pronouns to make sense of antecedents, and we have verb-tenses to understand one’s relation to time. But, if someone corrects your saw with a have seen, firstly, consider if you perhaps truly have made a mistake. Upon vindication, tell the offender that you’ll see him later, which doesn’t actually mean that you’ll see him later, if that isn’t obvious to him already—but, maybe, for obvious reasons, he’ll require the clarification.