I followed the link you provided to U.S. President Obama’s “Concert of Hope” speech and while I was impressed by his oratory, I agree with you that the two sentences you quoted from it indeed seem odd. On close analysis, in fact, they are flat-out grammatically wrong.
Take the first sentence you quoted, which is the topic sentence of the 8th paragraph of the speech (italicizations mine):
The sacrifices of these men and women, and of our military families, reminds us that the wages of war are great; that while service to our nation is full of glory, war itself is never glorious.
The subject of the main clause of that sentence is the noun phrase “the sacrifices of these men and women, and of our military families,” which on its face as a compound subject is obviously plural in form, thus requiring the verb to be plural in form as well—“remind” and not “reminds.” The grammar rule here is, of course, that when two or more singular nouns are compounded as subject or doer of the action—meaning they are added together or are acting together (or both, as in this case)—the operative verb should take the plural form.
Also, in linguistics, that noun phrase is called a
nominal group, which by definition consists of a particular noun (“sacrifices”) and all the other words that modify or characterize that noun. Within a clause, a nominal group functions as though it is that noun itself, which is referred to as
the head or head noun; the items that precede the head noun (in this case, the article “the”) are called its
premodifiers, and the items that come after it (“of these men and women, and of our military families “) are its
qualifiers. In a nominal group, the rule is that it’s the head noun that determines whether the noun phrase is singular or plural. Any other noun or pronoun found in the premodifier or in the qualifier of the head noun doesn’t determine or affect its being singular or plural. Clearly then, with “sacrifices” as the head noun of that nominal group, the operative verb should be in the plural form “remind” and the sentence in question should read as follows:
The sacrifices of these men and women, and of our military families, remind us that the wages of war are great; that while service to our nation is full of glory, war itself is never glorious.
Now let’s take a close look at the second sentence you quoted:
These past 10 years underscores the bonds between all Americans.
That sentence is actually the topic sentence of the 10th paragraph of President Obama’s speech. On its face, I think it’s grammatically wrong, for the doer of the action in that sentence is the obviously plural noun phrase “these past 10 years,” thus requiring the operative verb to be in the plural form “underscore” instead of the singular form “underscores.” There’s a debatable school of thought in English grammar, though, that considers as singular a noun or noun phrase denoting a period of time, like “five years” in the sentence “
Five years is not enough work experience to qualify you for that job.” In the usage of President Obama’s speech, however, it’s very clear from his use of the plural article “these” in that sentence that he meant to use the period “10 years” in the plural form. In fact, that sentence forms part of the following series of five topic sentences in the speech, all of which except the topic sentence of the 10th paragraph—the odd-man out among them and the very sentence in question here—use the time period “there past 10 years” in the plural form:
These past 10 years have shown that America does not give in to fear. (5th paragraph)
These past 10 years have shown America’s resolve to defend its citizens, and our way of life. (7th paragraph)
These 10 years have shown that we hold fast to our freedoms. (9th paragraph)
These past 10 years underscores the bonds between all Americans. (10th paragraph)
These past 10 years tell a story of our resilience. (11th paragraph)
Clearly, then, we can confidently say that the speech erred grammatically—if inadvertently—in the 10th paragraph by using the singular verb form “underscores” for the plural form “these past 10 years.” That sentence should be corrected as follows:
“These past 10 years
underscore the bonds between all Americans.”
FURTHER READING ON SUBJECT-VERB AGREEMENT:How to lick errors in subject-verb agreement for good
