Opiniatrety

The following blogger-sentence

"John has sent me this article. Click here"

doesn't imply that John is currently sending the speaker his article, but it does imply that at the time of speech it is the case that John sent his article in the past. Hence, the infelicity of

"John has sent me this article on Jan 13, 1983"

So, I think you are right.

Let me guess who the author of the sentence is.

Yeah, when I was teaching present perfect, you have to really emphasize to students that you can't use it along with a fixed time in the past (i.e., a time with an end-point).

But! Why is it that you can say, "I have seen it in the past"? Past is past; it's over. Or does "past" mean "up to the present moment"? It must mean the latter, or my example sentence would be ungrammatical.

I think the deal with "past" is that it precisely isn't a fixed time in the past, but rather all of it up to the present moment. The present perfect does seem to be one of the things about English grammar that second language learners have the most trouble with.

The present perfect isn't familiar to many USians who are native speakers, either. I have noticed. In the past.

Oy. To quote myself: when I was teaching present perfect, you have to really emphasize

Clearly, I have a shaky grasp on tenses myself. And I switched from "I" to "you."

I am mortified.

I have been mortified on Jan 13, 1983, and every Tuesday since.

My first reaction was to agree with you.

However I don't think there is any infelicity in:
This enemy is more dangerous than any we have faced in previous centuries.

How about:
This enemy is more dangerous than any we have faced in the nineteenth century or the twentieth century. (Seems ok?)

This enemy is more dangerous than any we have faced in the nineteenth century. (Seems odd?)

Neither of Richard's last two sentences work for me if we are in the twenty-first century.

Agreed with teo; none of them work for me unless you've been time-traveling and just came back from one of those centuries.

dagger, that's an interesting observation. It seems to me that you can use present perfect with any time interval that runs up to the present moment:

I've seen this expression three times in the last week/month/year/since 1983

so I think your explanation, that the past runs up to the present moment, sounds good.

Standpipe's sentence is interesting too. Given that today isn't Tuesday, it specifies a time period that stops before the present. And this can work even if it's known that last Tuesday was the last time:

The class has met on Sept. 5 and every Tuesday since but won't meet on Tuesdays anymore

Is that OK?

Also, note that you can specify the past time, but I think you need a comma:

We have faced more dangerous enemies, in 1941 and 1955.

But because of the comparative construction, even a comma won't save Santorum's original sentence. "In the 20th century" would attach to the main verb of the sentence, but that's present tense.

This enemy is more dangerous than any we have faced in the nineteenth century or the twentieth century.

Obviously, my acceptance of this sentence is predicated on interpreting "we" as something like "we the people of the United States of America," not something like "we in this room."

Perhaps you would find the sentence more acceptable if that interpretation of "we" had been encouraged (e.g., by previous sentences).

Nope, still no good. The sentence still implies that the time of utterance is during the twentieth century.

This enemy is more dangerous than any we (the people of the United States of America) faced in the thirteenth century.

I took out the "have," which is what is giving everybody fits. I also corrected the sentence to what Baron Richard de Santorum, Defender of the Faith, Most Holy Crusader, and Governor in the Papal Name of Acre and Jerusalem, meant to say.

Perhaps there is more weirdness. The sentence in question seems to imply that terrorism was not an enemy faced in the 20th century; for if it were, it would be more dangerous than itself, which is impossible. Isn't that weird?

Campbell, that's literally true, but I think it's pretty common to use "more blahblah than any..." when you mean "more blahblah than any other...." Either because the quantifier domain is implicitly restricted to exclude the thing that's most blahblah, or because the obvious falsehood of the literal statement means that it implicates 'many other'.