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Suppose we know that "terrorism is a serious crime".

And that "you have to report terrorism".

Can we say that

  • "you have to report a serious crime"?

I think that the bulleted statement is true. But I just took an, apparently, reputable reading comprehension test, which claimed, the point was not true despite the above.

If I'm right, which definition of "a", in that expression, makes it true?

closed as off-topic by Rory Alsop, RegDwigнt Mar 6 '16 at 16:16

  • This question does not appear to be about English language and usage within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

  • i mean ofc the statement is also false, but then i would have thought that every statement is false if we use whatever senses to the words we may like. in effect, that we "can tell" e.g. that balloons do not sleep furiously: nonsense is false and you can make anything nonsense – user3293056 Mar 6 '16 at 9:53
  • Your comment makes no sense to me. Are you asking whether both versions (with and without the article) are grammatical? Truth and falsity are semantic values. – deadrat Mar 6 '16 at 10:31
  • it's kinda irrelevant, maybe i should delete it. i was asking myself outloud if every or at least nearly all expressions can mean, with sound grammar, something untrue – user3293056 Mar 6 '16 at 10:34
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    If it helps, I'm not trying to be unhelpful. The five-word sentence I gave you is both grammatical and true. It's not nonsense. "Grammatically sound meaning" is hopelessly confused. Grammatical (which I think is what you mean by "grammatically sound") is about form. Meaning is about semantics. – deadrat Mar 6 '16 at 10:59
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    As others have pointed out, this is not a question about English, or specific to English. We don't have a dedicated site on logic yet. The closest we have to that is Math and Philosophy. You should check if they accept this kind of general question about basic logic. Or just read up on deduction. – RegDwigнt Mar 6 '16 at 16:16
4

This is more logic than English or grammar.

If something (X) is terrorism, then it is a serious crime. So T(X) implies S(x) where T(x) means x is a terrorism, and S(x) means x is a serious crime.

If something (X) is terrorism, then you have to report it. So T(X) implies R(x) where R(x) means you have to report x.

So we have two statements of the form

Forall x T(x) implies S(x)
Forall x T(x) implies R(x)

but we cannot deduce from this that

Forall x S(x) implies R(x)

It is easy to construct examples to show that we cannot infer 'S implies R' from 'T implies S' and 'T implies R'. For example if T is divisibility by 8, R is divisibility by 4 and S is divisibility by 2.

If, on the other hand, we had

Terrorism is a serious crime

and

You must report all serious crimes

then we could deduce that

You must report terrorism.

In this case, from 'P implies Q' and 'Q implies R', we may deduce 'P implies R'.

  • Hello, John. Your first statement is true, which makes this off-topic here on ELU. It is considered unacceptable to 'answer' questions recognised to be off-topic. – Edwin Ashworth Mar 6 '16 at 16:01
  • John, your answer is acceptable to me, and in fact, prompted me to understand the question. – deadrat Mar 6 '16 at 19:18

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