I realise that Math SE $\neq$ Philosophy SE, but what questions of logic can be posed? Particularly, can any question of logic involving symbols be asked here? (This is what I mean by 'symbolic logic' in the question title; please advise if I've erred).

Logic in Philosophy vs. Mathematical Logic inspired this question. I'm unversed in logic or philosophy, but am confused by the allowance of

1. Logic nonsense/paradox,
2. Why is predicate "all" as in all(SET) true if the SET is empty?,
3. Why is this true? $(\exists x)(P(x) \Rightarrow (\forall y) P(y))$,
4. Implies vs. Entails vs. Provable,
5. In classical logic, why is $(p\Rightarrow q)$ True if both $p$ and $q$ are False? ,

contrary to the closures of the following, NOT by reason of being duplicates:

6. https://math.stackexchange.com/a/867804/53259 (cp the answer which does employ symbols)
7. https://math.stackexchange.com/q/1038895/53259

  • 5
    $\begingroup$ If you are looking for consistency in the closure of questions on math se, you are in for a rude awakening. $\endgroup$ Mar 8 '15 at 6:00
  • 3
    $\begingroup$ Your first example of closed question doesn't contain any symbol, so I'm not sure how it can be classified as "symbolic logic". It seems rather to be a problem of interpreting a natural language sentence... Agree or disagree with the closure, but that's much more of a gray area. Your second example wasn't closed because of topicness, it was closed because it was "not a real question". And I agree, "do anyone here post any comments" is hardly a focused question that can be reasonably answered with a definitive answer... $\endgroup$ Mar 8 '15 at 8:52
  • $\begingroup$ @NajibIdrissi Thank you for your elucidation; I've enumerated the questions for clarity. About 6 (which you commented on), I had meant to refer to the answer, which does use symbols. About 7, I changed the question because I admit that I don't fully understand the amterial of the original. $\endgroup$
    – NNOX Apps
    Mar 8 '15 at 19:25
  • $\begingroup$ Note that the current #7 was not closed for being off-topic, but as "unclear what you're asking". Apparently the closevoters either couldn't recognize the kind of puzzle from the OP's description, or they felt it to be ill-defined what it was he was asking about those puzzles. If it's the latter, I tend to agree with them, even though I took a shot at answering -- while I was writing it turned out that the OP already seemed to know that the problem type corresponds to a SAT variant, so I'm wondering too which kind of answer he expected. $\endgroup$ Mar 8 '15 at 23:11
  • 3
    $\begingroup$ Symbolic logic $\neq$ "logic involving symbols". Symbolic logic to a mathematician is apt to mean the study of logic formalized with symbols. The first-order logic known as "predicate calculus" is a well-studied system of this kind. Philosophers now tend to adopt this "artificial language" approach in order to avoid ambiguity. Your example 7 seems more of a combinatorics problem. $\endgroup$
    – hardmath
    Mar 9 '15 at 13:39

As far as subject matter goes, symbolic logic is certainly within the scope of Math.SE. However there are other criteria that could make a Question about symbolic logic off-topic here.

Community members are exercising judgement in each close vote cast; it's not an automated decision. So an element of subjective opinion on each vote is inevitable.

That granted, the most common situation I vote to close as off-topic Questions about math-related problems is that the post lacks a sufficient context. The poser may in the extreme merely have posted a cellphone image of a homework assignment before reading it in enough detail to understand what the problem is about.

In this regard I look for some indication that a Question reflects at least a first effort on the part of the OP to solve it themselves.


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