Questions pertaining to logical constructs

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42
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“Childlessness is hereditary in our family” What do you call a statement containing a contradiction such as the example?

This kind of sentence is usually absurd and may or may not be recognized as such by the person who utters it. She will regret it till the day she dies, if she lives that long! "Aren't you going to ...
21
votes
10answers
5k views

Is “I believe x does not equal y” the same as “I don't believe x equals y”

Given x and y could be any phrase, do these phrases always mean the same thing? If not, what's the difference? I believe x does not equal y I don't believe x equals y
19
votes
7answers
18k views

“All that is gold does not glitter”

"All that is gold does not glitter" is the first line of a poem from the Lord of the Rings and it's supposed to mean "not all gold glitters" but I'm struggling to see how this can be deduced. If all ...
19
votes
8answers
18k views

Does “either A or B ” preclude “both A and B”?

In mathematics, "A or B" includes "A and B". Does "either" mean "A or B but not (A and B)" or does it include the possibility of "A and B"? The context might be mathematics, formal logic or ordinary ...
18
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6answers
2k views

Is there a name for an argument that is also a counter-argument?

A person states an argument to support a position, but that argument could equally support the opposite position. Is there a name for such an argument? Or a phrase to describe the concept?
13
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2answers
321 views

Where did the practice of using quotation marks to discredit an opponent (“scare-quotes”) come from?

This is a practice extremely prevalent on conspiracy theory blogs and social media (a.k.a., conspiracy theory blogs), but where did the concept of discrediting opponents with quotation marks come from?...
12
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7answers
5k views

Does 'some' necessarily imply 'not all'?

If some X's are Y's, does that imply that some X's are not Y's?
11
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6answers
1k views

What's the term for denying something so as to raise doubt?

Topical example: 'There was a scuffle outside the local pub. There appears to be no connection with religious extremists.' ...but now you're wondering if there was. It's a nasty tactic used to raise ...
11
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4answers
394 views

Does the word “and” always mean a logical (boolean) operation?

For a simple phrase like "macaroni and cheese" it's clear you want both macaroni and cheese, not one or the other. But as more and more words are added, I've noticed a tendency to begin to read "and" ...
10
votes
8answers
8k views

Word/phrase/idiom to describe avoiding answering a question by stating the question doesn't need to be asked

I run into this situation often in the office. I have a specific question to ask somebody and have chosen the person to ask it, but that person doesn't know the answer. Instead of answering the ...
10
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5answers
27k views

“If” vs “Only if” vs “If and only if”

If I said: Yell only if I fall. Would the person have to yell once I fell? Sources of confusion Wikipedia This guy
9
votes
7answers
1k views

Word or term for an argument that is inherently true

What do you call an argument/position that is impossible to counter because it depends on undefined adjectives/adverbs? Examples: Good websites are the ones that are effectively designed. ...
9
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9answers
38k views

“Neither can live while the other survives”— does it make logical sense?

At the end of the fifth book of Harry Potter, "The Order of Phoenix", there is a prophecy concerning Harry Potter and Lord Voldemort: The one with the power to vanquish the Dark Lord ( Lord ...
9
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5answers
108k views

“Centered on” or “centered around”

I have often heard presenters talking about something centered around another thing, but it seems a bit illogical and hence improper to talk like this. Am I right about this?
8
votes
1answer
8k views

Difference between “subsequently” and “consequently”?

When studying and reading course material in "softer" sciences that are descriptive the word "subsequently" appears in a way like "and subsequently" ...what does it mean, disctinct from "consequently" ...
7
votes
6answers
825 views

The “Since… then” construction

Is the construction "Since... then" correct? E.g. Since it's a right triangle, then the Pythagorean theorem holds. It sounds and feels wrong to me, and I think someone once told me it's wrong, ...
7
votes
5answers
699 views

Does this logical fallacy have a name?

A phrase being used by the "news" media regarding the recent arrest of people in Columbus, NM is "firearms favored by the Mexican cartels", referring to their purchase of AK47s and other ...
6
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5answers
3k views

Can I say “We don't must”, any alternative using a modal verb if I can't?

Let me explain. Suppose someone says "We must play a game now". I disagree, but only on that we have to do it. I shouldn't answer "We must not" because I would be saying that the game is not to be ...
6
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3answers
663 views

Is there a term for it when you use an obviously false statement to highlight the falsity or absurdity of another?

For example, person A states something. Person B says "And pigs fly" to imply person A was wrong. If there's no term for it, what could you call that that sounds smart?
6
votes
2answers
751 views

“There is no doubt this is arguably wrong”

This is from a review of something: There is no doubt that the (product name) is arguably the best consumer (product category name) currently on the market. I stopped for a while after reading ...
6
votes
6answers
963 views

The word 'not' often doesn't mean total negation in mathematical sense?

Consider the following conversations: X1: I paid $10 for that hamburger. Y1: That's not cheap! X2: I pay $1 for broadband Internet access. Y2: That's cheap! X3: I paid $1 for a hot ...
6
votes
3answers
833 views

Difference between “not every” and “every … is not”

I've always understood that you can order the words not and every (or similar words) in the following two ways to convey distinct logical meanings. Every human is not a man. There is no human being ...
6
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1answer
229 views

Historical frequency of expression “and/or”: Corpus search

What is the historical frequency of the expression “and/or”? I have a feeling that I almost never see it in older texts, but that it is has become exponentially common in the past five or ten years. ...
6
votes
2answers
2k views

Would the rejection of an argument because of a grammatical error be a type of logical fallacy?

Many people may have experienced situations (often online) where someone dismisses another's argument not on the merits of the argument, but because of a grammatical (or, more generally, mechanical) ...
5
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5answers
5k views

The size of my confusion is “second to none”

Why "second to none" is being considered as "the best" instead of "the worst" (almost non existent)? To my understanding - "none" is "nonexistent", while "second to none" should be... well... almost ...
5
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2answers
870 views

Is it correct to use “or” in place of “and/or”?

Consider the following sentence: A project is a large and/or complex undertaking. To me, the expression “and/or” seems redundant since in formal logic “or” implies “...
5
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6answers
1k views

Is there a common English phrase for the 'so absurd it must be true' logical fallacy?

There are various common (often Latin) phrases for various logic fallacies, such as post hoc ergo propter hoc, argumentum ad populum, slippery slope fallacy, etc. Is there a common phrase used to ...
5
votes
4answers
894 views

Adjective to describe “just because… doesn't necessarily mean…”

This is one of those phrases used very commonly (and apparently subject to lots of scrutiny on this website), but is difficult to define and also far too long to submit to a reverse dictionary. Let's ...
5
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3answers
395 views

At least two or more: Not always redundant?

At least two or more Is the “or more” bit above ever not redundant? Seems absolutely redundant to me, but it gets about 170 million Google hits, and many from government sites and university sites.
4
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3answers
2k views

Is it really possible to be “half dead”?

It is not all-too-rare to hear of someone being "half-dead," but is that logical, or possible? If so, how do you determine just how dead, percentage-wise, a person is? If it's possible to be 50% ...
4
votes
3answers
1k views

'Therefore' in an illogical logic sense

I have a co-worker that is always saying "Therefore, A B C" when the "A B C" isn't a conclusion from any sort of deductive reasoning. For example, Me: ... thus, that's how it works. Her: I ...
4
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2answers
386 views

Is it true that

Is the following sentence grammatically incorrect? Is it true that 1+1=2 ? I know it is easier to say: Is 1+1=2 true?
4
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2answers
1k views

Does the plural include the singular?

Does the plural include the singular? And if so, in what sort of cases? This question has arisen because of the example sentence below. Amendment shall be permitted only in cases of: 1. deletion ...
4
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2answers
364 views

What fallacy is this? “Your argument is wrong/invalid because it's just an opinion.”

I encounter this fallacy frequently in online discussions where an opponent completely disregards all of my premises and says my conclusion is invalid because it's an "opinion" and "not objective." ...
4
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4answers
306 views

What is the name of the “agency” fallacy?

I'm looking for the name of the logical fallacy where intent or agency is assumed when in fact there is none. It's a common fallacy in my experience, but I can't seem to find it described ...
4
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4answers
1k views

What's the logical fallacy where people dismiss what you say as irrelevant to the real-world?

Quite often I see derision about ideas by people who label them as 'too academic'. Often this appears to result from laziness or an unwillingness to stretch their thinking. What's the logical ...
4
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2answers
1k views

What's the difference between “Not Completely True” and “Completely Not True”?

From what I understand, in second order propositional logic, ∀¬x and ¬∀x are equivalent statements. Apparently these are not equal. ¬∀x ≡ ∃¬x However, rendered into the English language, consider ...
4
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2answers
3k views

Cut the lights on

This expression is commonly used in the southern United States from Oklahoma to Virginia, and is patently illogical, and yet fails to inspire any consternation or lack of semantic connection. On a ...
4
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2answers
514 views

Hypernym for “conjunction” and “disjunction”

Is there a hypernym for conjunction and disjunction, in their logical senses? Just using "junction" doesn't seem right to me.
4
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1answer
81 views

Use of “and” and “or” in lists when intent is to dissallow all items

Sometimes it is unclear to me whether "or" or "and" should be used in a list. For example I have seen the following lease agreement: The dwelling may not be used for illegal activities: including ...
3
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4answers
791 views

Overuse of “however” in my scientific writing? [closed]

In scientific writing, I always feel the need to logically connect all my sentences to have a clear logical path between beginning and end of a paragraph, else it is just feels like a list of random ...
3
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4answers
2k views

A word for when two statements are both true or both false

Is there a word which basically means that there are two statements that are both true, or both false, but not one true and one false? In computing, we call this a bitwise and. 3 * 3 = 9 4 * 4 = 16 ...
3
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2answers
2k views

Usage of “if and only if” as a nontechnical term

The phrase "if and only if" (iff) is commonly used in the field of mathematics (⇔) and computer programming, as a conditional expression in classical (Boolean) logic. Within that scope, it might not ...
3
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4answers
200 views

How to succinctly and clearly connote the reverse of a statement

Here's a published example of a problem I come across frequently: A cop is six times more likely to be shot by someone black than the opposite. Let us assume that the writer meant to say: ...
3
votes
2answers
49 views

What's the name for when a layman thinks a technical task is easier than it actually is?

As a software engineer, my job is highly technical. A co-worker and I were remarking that frequently our non-technical co-workers will assume that we're not working if a task takes longer than they ...
3
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3answers
127 views

What is the word for an arbitrary simple example, typically used with proofs?

Typical usage is with math, or philosophy, proofs. Also typically the simple example disproves the theory, but is of a arbitrarily contrived nature and not something that would naturally arise. Is ...
2
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2answers
580 views

Unambiguous Way of Stating a Biconditional in Plain English

I am having a hard time understanding this section in Wikipedia's article on Logical biconditionals: Colloquial usage One unambiguous way of stating a biconditional in plain English is of the ...
2
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4answers
238 views

GRE Sentence Completion Question

Select the two answer choices that, when used to complete the sentence, fit the meaning of the sentence as a whole and produce completed sentences that are alike in meaning. As my eyesight began ...
2
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3answers
5k views

What does “an A/B metaphor” mean?

I wonder what "an A/B metaphor" means, for example, in the following quote from Wikipedia about formal language: "In some applications, especially in logic, the alphabet is also known as the ...
2
votes
4answers
869 views

What is the verb form of “conjunction” in the logical sense?

In logic and computer programming, a conjunction of two logical statements is said to be true if and only if both statements are themselves true. For instance: "The sky is blue" and "the grass is ...