One Man's Modus Ponens (Is Another Man's Modus Tollens) 

Haha! That's great!

I would say so. Moore is basically saying that q is absurd, so he rejects the argument based on the conclusion.

Reductio ad absurdum is similar, but slightly different. Generally reductio ad absurdum arguments take either the conclusion or one of the premises, and show that they lead to a contradiction or (in the less formal use of the phrase) lead to a particularly ridiculous conclusion. So it woudl look like: P1: p P2: p implies q C1: therefore q P3: q implies r P4: q implies not r P5: r and not r C2: therefore not q. However, if you take the less formal definition which requires that you show an argument lead to an absurd conclusion and you think that the conclusion itself (i.e. q) is absurd, it might be considered an example of this. It could also be used in combination if you showed that q implies a contradiction then you use that to specifically deny p via modus tollens.

@@CarneadesOfCyrene So every modus tollens is a reductio ad absurdum, but not every reductio ad absurdum is a modus tollens?

@@nosteinnogate7305 I think you got it reversed. All reductio ad absurdum is modus tollens.

Yep. Often the problem is the implication itself.

​@@CarneadesOfCyrene I found it fascinating, how Maverick Christian defended this and other similar implications of his: _"A material implication is only false, if the antecedent is true and the consequent is false._ _You need to show, that this is the case in order to that premise to be false."_ I gave him an analogy with a _modus tollens_ about a drawn quadrilateral: *1. If it's possible for a drawn quadrilateral to be a rectangle, then it's possible for that drawn quadrilateral to be a square.* Suppose we get the hint, that the quadrilateral is definitely not a square. Hence, premise 2. It's not possible for that drawn quadrilateral to be a square. (conclusion from 1 and 2 via _modus tollens_ ) 3. Therefore, it's not possible for that drawn quadrilateral to be a rectangle. Yet that drawn quadrilateral is a rectangle and not a square, because I, the person, who drew that quadrilateral, specifically drew that quadrilateral that way to demonstrate the absurdness of these kinds of logical inferences. I think, that this has to do with aristotelian logic or the lack of considerations of aristotelian logic: Squares and rectangles are defined in such a way, that the set of all squares is a subset of the set of all rectangles - meaning, that all squares are rectangles, *but not all rectangles are squares* . So if a quadrilateral is a square, then that quadrilateral is a rectangle since all squares are rectangles. *But it's not necessarily the case, that if a quadrilateral is a rectangle, then that quadrilateral is also a square since not all rectangles are squares.* So those kinds of implications are on their own simply false. They might work with other and more assertions, assumptions, informations and premises, but on their own they are simply irrational to hold. This irrationality holds for a lot of implications; not just made by apologetics but also quite a few other not-well-trained in logic philosophers and persons. Also this irrationality holds for at least one supposedly well-trained in logic mathematician and philosopher - namely Alexander Pruss: _1. If there could be a backwards infinite sequence of events, Hilbert's Hotel would be possible._ *_2. If Hilbert's Hotel were possible, the GR Paradox could happen._* _3. The GR Paradox cannot happen._ _4. Therefore, there cannot be a backwards infinite sequence of events._ from his blog post *"From the Grim Reaper paradox to the Kalaam argument"* (Friday, October 2, 2009) No, the GR Paradox could happen only if Hilbert's Hotel were possible - meaning if the Hilbert's Hotel were not possible, then GR Paradox could not happen and if the GR Paradox could happen, then Hilbert's Hotel were possible. Cause of something, drawn quadrilaterals, something, aristotelian logic, something, analogous,... This is my elaboration for you on, why sometimes (in my experience encountering apologetic arguments quite more than "sometimes") the "Third Way" is a justified rational way. You hinted in your video, that the “Third Way” might be a controversial one to do. Certainly it is controversial to do, if doing so would be unjustified and irrational. But in my experience with apologetic arguments the “Third Way” denying and rejecting that crucial implication is very much so and quite often justifiable and rational to do so.

Would you like a green quarter?

@@lbdeuce Actually, I was just going to STFU. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-H0OaeMYTbs4.html

It only works when you think you have a strong argument for q and you think your opponent has a weak argument for p. But generally yes, as a skeptic I find Moore's argument completely unconvincing. That said, it is a common argument style that you will see, particularly when faced with trilemmas that include an implication.