collinsdictionary.com:
(1) 'Cat' has a final 't'.
The letter "t" is the only one in the word "cat".
Then why is it possible to use "a" here?
my variant:
(2) 'Cat' has the final 't'.
Is (2) correct?
If not , then why not?
If it is, then what is the difference between (1) and (2)?
In short, because there are many final 't's. Bat, cat, format, splat — each has a final 't'. That means that cat's final 't' in this sense is one of many, which we express with the indefinite article.
If you're referring specifically to the 't' in "cat", then you would use the definite article:
No, 1 is better. We choose between "a" and "the" based partly on context. Consider this:
The house has a cat in it. The cat is black.
There is only one cat. And in the second sentence, we use "the" because we're talking about a specific cat. But in the first sentence, we're still establishing that context. We really mean "the house has one single instance of the category 'cat' in it," so we say "a cat" for that one.
Similarly, it makes sense to say "the word cat has a t in it." Having established that context, we might use "the" if we continue to discuss that letter that we just identified: "The t is the final letter."
EDIT: As I think about this more, I was puzzled why you might think that having "only one" of something would call for "the." After all, there are plenty of times that there would be just one of something, but "the" would be wrong. "There is a tree in our yard." Just one tree, but we wouldn't say "There is the tree in our yard." (Well, unless we were pointing at it.) I think maybe the source of your confusion is about proper nouns vs common nouns. There is only one Eiffel Tower. Ignoring replicas and models, there is only one "true" one in the world, and whenever we talk about it, we're talking about that one. In Paris, you would not say "Look, an Eiffel Tower!" With proper nouns we use "the" because we've already specified the single thing we're talking about. But cats, trees, and the letter "t" are common nouns. There are many cats, trees, and letter "t"s. We would use "a" when first identifying an instance, of them, and then could use "the" after having focused on that specific instance.
Remember, in the case of a definite article, you're indicating a specific thing.
If you're playing a word game in which you're making words up from a pile of letters, and you use the last letter "t" in the game to end the word "Cat", and someone asks you, "Where did the last 't' go?!?!?"
In that case, it would be perfectly accurate to say, "'Cat' has the final 't'." There may have been many 't's in the game, but that's the one you're talking about.
Otherwise, even though you're talking about the last 't' in 'cat', that 't' is a generic 't' that could be replaced with any other 't', so it wouldn't be proper to refer to it with a definite article.
While the word cat only has one t, there are lots of (letters) t in different words.
In this sentence, a is correct instead of the because the t in that word is just one of many used in many words.
Using the would imply that no other word is spelled with a letter t.
The sentences "'Cat' has a final 't.'" and "'Cat' has the final 't.'" are both plausible, but the one with "a" is much more likely, and the two sentences have different meanings.
The predicate "has a final 't'" expresses the normal, expected meaning: it is saying that there is a 't' there at the end. The sentence "'Cat' has a final 't.'" is essentially saying, "If you look at the last letter of the word 'cat,' you will notice that it is a 't.'"
On the other hand, the predicate "has the final 't'" is saying that something has that one particular 't' on the end of it. So one possible meaning of the sentence "'Cat' has the final 't.'" is, "If you look at the last letter of the word 'cat,' you will notice that it is that 't' that I mentioned a few minutes ago." Of course, that interpretation makes sense only if you really did mention a particular 't' a few minutes ago, and only if you intend to talk about that particular 't' again.
Another possible meaning of the sentence "'Cat' has the final 't.'" is, "If you look at the last letter of the word 'cat,' you will notice that it is the 't' which is the last letter of the word 'cat.'" But this is quite a strange thing to say, because it's completely unnecessary to point out that the word "cat" ends with the letter it ends with.
To summarize, the sentence "'Cat' has the final 't.'" is an unusual sentence that you would only say in unusual circumstances; the sentence "'Cat' has a final 't.'" is the correct sentence for expressing the usual meaning.
