This is commonly denoted as optional:
available as a choice but not required
The definition of a method, constructor, indexer, or delegate can specify that its parameters are required or that they are optional. Any call must provide arguments for all required parameters, but can omit arguments for optional ...
Such quips have always been popular; recall Mark Twain on the important role of the historian as storyteller, because
Very few things happen at the right time, and the rest do not happen at all.
Groucho Marx opens his first autobiography admitting that
I was born at a very early age.
and remarks in a letter that
I don’t care to belong to any ...
No, strictly, they do not convey the same meaning. In practice, your second sentence is often used to mean the first.
I believe x does not equal y means that you actually hold a belief about the inequality of x and y.
I don't believe that x equals y simply means that a belief about the equality exists, but you do not share that belief.
If you substitute ...
Let's start with pointing out that mathematics and formal logic are two things that do not apply to natural language in the sense that one can not follow clear rules to simply translate a statement in a natural language into some logical construct following simple rules. One has to understand the semantics of the natural language, and often, context is ...
Something that is allowed to be missing is omissible. Wordreference.com defines omissible as:
capable of being or allowed to be omitted
In English grammar the object relative pronoun is omissible:
The book (that) I wanted to buy was sold-out.
An appeal to extremes is an often fallacious application of reductio ad absurdum where one takes an argument to an extreme and neglects the actual circumstances or implications of the initial statement. As the website Logically Fallacious describes it:
If X is true, then Y must also be true (where Y is the extreme of X).
There is no way those Girl ...
The actual term is Irish Bull. (Credit to Centaurus based on our discussion and choster for the related and detailed answer). In the question, it is mentioned that it may not be recognized as such by the person who utters it. An irish bull can have oxymoronic, self-contradictory or paradoxical elements in it but it is actually an absurd statement, so it ...
You're correct, it is indeed contradictory. Taken purely logically, then, if neither can live while the other survives, then if Harry is alive Voldemort must be dead and if Voldemort is alive Harry must be dead. Since we know both Harry and Voldemort are alive, the statement is clearly false. Since the statement is part of a piece that refers to them as ...
Since is synonymous to because in this case.
Your sentence is therefore equivalent to
*Because it's a right triangle, then the Pythagorean theorem holds.
There are two words indicating a causal relationship, because and then. That's one too many.
You can use either of these two:
Since it's a right triangle, the Pythagorean theorem holds.
If it's a ...
If "every" is in the scope of "not", it means "It is not the case that every boy ran," or, that is, "Some boy didn't run," or "Not every boy ran." That is the preferred interpretation if every is focused or emphasized: "Every boy didn't run" with rising intonation at the end.
If "not" is in the scope of "every", it means "For every boy it is true that that ...
The original was actually Shakespeare: all that glisters is not gold, but that needn't concern us here.
OP has simply misparsed the sentence - it actually means "Not everything that is gold glitters" (which is to say, "There are some things which are gold that don't glitter").
You can always Google "every x is not y" for more discussion of why this type of ...
Languages are not formal logic systems, and words do not derive their meanings from the definitions in dictionaries. If they did, then your argument would mean something, but as it is what you have is an amusing but pointless exercise.
Words derive their meanings from their shared usage in a linguistic community, and those meanings are ultimately grounded ...
One relevant term from logic:
red herring — The idiom "red herring" is used to refer to something that misleads or distracts from the relevant or important issue.
Specific forms of red herring exist and I find that appeal to motive fits nicely:
appeal to motive — Appeal to motive is a pattern of argument which consists in challenging a ...
This is the Cooperative Principle in action:
(link to comic)
If you have no particular reason to think I will buy you a wallet and I say:
I will buy you a new wallet if you need one.
then, under the Cooperative Principle, you can safely assume that this is all you want / need to know. But if there were other conditions in which I'd buy you a wallet, ...
In Standard English, even if a sentence is completely negative in sense, we apply negation only once, at the first possible place. So, for example, the following sentences all mean the same thing:
None of them ever found any of it anywhere.
Never did any of them find any of it anywhere.
None of it was ever found anywhere by any of them.
Nowhere did any of ...
The usual mathematical terms for these things (from the study of modal logic) are 'necessary' (for your 'guaranteed') and 'possible' (for your 'allowed'). All you need is negation to get all four possiblities.
necessary - it must exist
possible - it may exist
not necessary - it may not exist
not possible - it cannot exist
Depending on your (choice of) ...
One term possibly applied to such statements is a "paradox".
Apparently, it comes from the greek word 'paradoxon', meaning contrary to expectations (http://literarydevices.net/paradox/).
Some examples that come to mind are:
You should read a book on how to treat your illiteracy.
There is no worse feeling than apathy.
The or of English is not equivalent to the or of formal logic. In many cases, English or actually means the exclusive or of logic. For instance, if you say:
Turn left or right at the intersection.
it’s exclusive, because it’s not possible to do both. Or you might ask:
Are you having a boy or a girl?
(Although a logician having fraternal twins might ...
A literal oxymoron - is a figure of speech that juxtaposes elements that appear to be contradictory in some cases exposing a paradox.
Childlessness - not having children
Hereditary - features passed on through act of childbirth
Does the word “and” always mean a logical (boolean) operation?
Certainly not, a quick glance at the dictionary demonstrates that the use of and is not limited to a boolean operation:
1.0 Used to connect words of the same part of speech, clauses, or sentences, that are to be taken jointly:
bread and butter
they can read and write
As Lawrence notes, such a word is heterological.
A word that does not apply to itself
By contrast a word which does describe itself is autological or homological.
The word heterological is not merely "paradoxical" in that it describes words which don't describe themselves, it also leads to a paradox all of its ...
You might consider this as a case of ignoratio elenchi, where an irrelevant argument is presented as an answer to the question at hand:
Ignoratio elenchi, also known as irrelevant conclusion, is the informal fallacy of presenting an argument that may or may not be logically valid, but fails nonetheless to address the issue in question.
[...] The ...
The quote would be clearer if it spoke of the difference between the reading in which all boys didn’t run and (that in which) some did.
In the positive version “every boy ran”, there is no ambiguity: 100% of the boys ran.
Logically, “every boy didn’t run” follows the same pattern: for each boy x, the statement asserts that x didn’t run. That is, the ...
This question is confusing as hell, but I think "unnecessary" or any of its synonyms might fit, depending on what you mean exactly, as I'm confused.
Something is allowed. (allowed to exist) Something is
unnecessary (allowed to be missing)
You also have the condition:
Also, if I say that something is not ??? (allowed to be missing), then
it is ...
It means not everything that is gold glitters. Tolkien undoubtedly was borrowing from Shakespeare here, specifically the poem that one of Portia's suitors discovers when he reads the scroll associated with the golden chest that he has (to his loss) chosen:
“All that glisters is not gold—
Often have you heard that told.
Many a man his life hath sold