75
votes
Accepted
If I said I had $100 when asked, but I actually had $200, would I be lying by omission?
I would say it depends on the situation. Specifically, it depends on whether the person asking you the question wants to know whether you have at least $100, or exactly $100. The question could ...
- 29k
44
votes
If I said I had $100 when asked, but I actually had $200, would I be lying by omission?
tl;dr- It's a lie if the speaker intends to deceive the listener(s).
More specifically, it's a lie-by-omission if the speaker intends to deceive the listener(s) by neglecting to mention something ...
- 1,995
36
votes
Accepted
Why is it that the statement "All goblins are yellow" does not contradict the statement "All goblins are pink?"
Edit in response to your comment: Okay, long answer:
What is the meaning of "the"?
(A previous version of the question had the statement "The goblins are pink"; this is an ...
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34
votes
Accepted
Do computers use logic?
Allow me to be precise about this. Logic (in the formal sense) is a system of manipulating symbols according to rules. Computers can manipulate symbols according to rules — that is more or less ...
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26
votes
Accepted
If you used intuitionistic logic in real life, would you not sound absurd?
As Conifold comments, a real-life intuitionist would not shy away from assuming LEM ... when appropriate. Intuitionism merely permits the failure of LEM, it doesn't assert that it always occurs. For ...
- 3,368
22
votes
Why isn't the Liar's Paradox just accepted to be complete nonsense?
You ask:
Why isn't the Liar's Paradox just accepted to be complete nonsense?
You want an answer in "plain English." The easy explanation is that "complete nonsense" intuitively ...
- 31.6k
21
votes
Accepted
Why did the mid-19th century and earlier thinkers fixate on one-place predicates?
Because there was a calculus for one-place predicates, Aristotle's syllogistic, roughly equivalent to monadic predicate calculus. Aristotle does discuss "relatives" in Categories, which ...
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17
votes
Why is it that the statement "All goblins are yellow" does not contradict the statement "All goblins are pink?"
There are two ways in which these statements can be non-contradictory:
Option A: Non-mutually exclusive
It is possible for a goblin to be both pink and yellow, therefore it is possible for a goblin to ...
- 171
15
votes
Accepted
Why are there two fundamental laws of logic?
They're not equivalent, but they do seem very close together in most contexts when you assume a bivalent (two truth valued) logic.
But they pull apart when it comes to several controversial ...
14
votes
Why did we define vacuous statements as true rather than false?
We do NOT define vacuous statements as true.
A vacuously true statement is vacuously true.
A "vacuously false" statement is vacuously false; although nobody ever gives this type of statement any ...
- 2,995
14
votes
Has Münchhausen's trilemma been solved?
The Muenchhausen Trilemma is a philosophical insight, not a philosophical problem. Hence there is no need for a solution, but the call for application.
The trilemma was formulated by Hans Albert. It ...
- 37k
14
votes
Accepted
Can it be proven from pure logic that at least one thing exists?
To expand a little on causative's comment. In standard logic, it is a convention to assume that the universe of quantification is non-empty, which is to say that at least one thing exists. It we don't ...
- 29k
13
votes
Can it be proven from pure logic that at least one thing exists?
Just the fact that you are pondering this question confirms that you exist – according to Descartes, see Cogito ergo sum.
Also Anselm considered his ontological argument to be a proof of the existence ...
- 37k
12
votes
Accepted
What is the axiom of reducibility? And what philosophical controversies did it incite?
To put it in simple words we have to describe in a couple of words the project of Principia Mathematica, which Russell inherited from Frege: reconstructing mathematics from logic alone. For a broader ...
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12
votes
Do premises need to be valid conclusions?
Validity in logic is a somewhat tricky notion to understand as it is different – though only subtly – from related, pre-theoretic notions. For instance, not every valid argument is ‘convincing’ or ‘...
- 753
11
votes
Accepted
How come intuitive thinking is related to constructing a proof?
Intuitionism is a philosophy of mathematics that was introduced by the Dutch mathematician Luitzen Egbertus Jan Brouwer (1881–1966): he developed a very personal philosophy of mathematics that founds ...
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11
votes
What is the difference between 'accidental' and 'contingent'?
Colloquial meanings of the two words are pretty close, accidental is "occurring unexpectedly or by chance", contingent is "subject to chance; occurring or existing only if (certain circumstances) are ...
- 43.7k
10
votes
Is finding truth possible?
You've stumbled upon an old problem in philosophy, The Paradox of Inquiry, first formulated in Plato's Meno.
The problem can be reformulated as follows:
Either you know the answer to a question, or ...
- 6,616
10
votes
Accepted
Is there an English language example where modus tollens is valid but contraposition is not valid?
Here's the example from David Lewis's Counterfactuals (1973):
If Boris had gone to the party, Olga would have gone.
Now suppose that Boris wants to go, but not if Olga goes, because he wants to ...
- 6,616
10
votes
If I said I had $100 when asked, but I actually had $200, would I be lying by omission?
Your question is about lying by omission, and this requires that you define lying. The definition I use is a communication with the intent to deceive. Thus, whether or not you are lying is a function ...
- 31.6k
10
votes
If you used intuitionistic logic in real life, would you not sound absurd?
Propositions in intuitionistic logic are probably best understood as statements about provability. P ʌ Q means that you can prove P and prove Q, ¬P means that from P you can derive a contradiction, ∃x....
- 1,298
10
votes
Is there a system of logic which denies DNI?
Yes there is. As you say, intuitionistic logic has DNI but not DNE. There are also dual-intuitionistic logics whose connectives operate in a fashion that is dual to those of intuitionistic logic. Dual-...
- 29k
9
votes
Accepted
What are the differences between philosophies presupposing one Logic versus many logics?
It is more complicated than a merely instrumental/metaphysical division. The "logics as mere instruments" were not meaningful until well into the 20th century, after the general ...
- 43.7k
9
votes
Do logically incoherent statements still have meaning?
My reading of Carnap's "The Elimination of Metaphysics Through Logical Analysis of Language" suggests to me that it is possible to form sentences in a language that are grammatically correct but ...
- 27.7k
9
votes
Is it logically permissible to neither believe nor disbelieve a proposition X? Or does this violate the law of excluded middle?
You seem to confuse belief (which is subjective) and the actual truth value of a proposition. The LEM only applies to the latter, not to the former. If you wish to stay inside a mathematical framework,...
- 474
8
votes
Accepted
Does the Fallacy Fallacy make logic useless?
Short answer: definitely no, that does not make logic useless.
When someone makes an invalid argument, they're committing some sort of a formal fallacy. That is only to say that the conclusion does ...
- 6,616
8
votes
Accepted
Logic and Computation: a philosophical viewpoint on Curry-Howard isomorphism
I think you are right to be impressed with the Curry-Howard correspondence. It is a detailed and extensive rule-by-rule and feature-by-feature isomorphism. This strongly suggests that proof and ...
- 29k
8
votes
What are lucid examples of non-truth functionals?
Conditionals in English are used for a lot more than just expressing simple truth functions. Here are some general cases where the truth functional material conditional doesn't fit.
Claims about ...
- 29k
8
votes
What, at present, are the major unsolved problems of logic?
One should keep in mind that the meaning of "logic" changed over the last century, and is now more confined to formal logic, although it is broader than deductive or mathematical logic in the narrow ...
- 43.7k
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