Questions pertaining to logical constructs

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18
votes
7answers
17k 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 ...
19
votes
7answers
17k 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 ...
2
votes
2answers
304 views

Ambiguity in Negation: “John did not come because of the rain”

John did not come because of the rain. This sentence seems to allow the following two completely different interpretations. John did not come. And the reason was the rain. John came. But the ...
1
vote
3answers
650 views

How do definitions of words imbue meaning? [closed]

How do definitions of words imbue meaning? To give you a gist of what I try to discover, I'll define a collection of sets of words and show that their intersection contains all 'circular defined' ...
10
votes
5answers
25k 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
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 ...
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
11
votes
4answers
375 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" ...
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" ...
6
votes
3answers
618 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
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 ...
4
votes
1answer
63 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 ...
4
votes
2answers
306 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
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 ...
3
votes
4answers
655 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 ...