Philosophy Now Forum

If I say 'I cannot conceive of a morally perfect world in which one exercises power over another, against their will, even though they are harming no one' it all rests on my definition of 'morally perfect world.' Either the phrase is meaningless as question begging (we are examining 'moral perfecti...

We assume that there are worlds where everyone does what they ought to do. OK, but are there more than one of these worlds? Of course you have to say yes, to make it fit the formal model - but does it have anything to do with your theory of morality? I don't see anything problematic about this. At ...

'Possible worlds' makes sense in the context of modal logic, which involves necessity and possibility. Technically, modal logic isn't inherently a logic of necessity and possibility, it's just a formal apparatus that can be used to analyse the concepts of necessity and possibility (among other thin...

I think you are actually criticising two different elements of my argument. I want to address this one first before we get to anything else though: I don't just say '~P' full stop, that would be like saying "◊~P at world w, therefore ~P at world w". What I'm saying, rather, is "◊~P at...

A common and useful way to think of the accessibility relation is like this: if world x is accessible from world w then, from the point of view of the inhabitants of world w, the happenings in world x are possible. However, my argument is a moral argument, and therefore requires us to use deontic l...

you perform a slight of hand: 2. ◊~P, world w According to (2), it is permissible not to act rationally. This means that there is some world x where ~P is true: 3. ~P, world x And similarly elsewhere. You don't give conditions to convert your modal operators to non-modal. It does not make sense to ...

I think it is circular, given that "'p is false' leads to a contradiction" is equivalent to 'p is true.' I don't think the logical equivalence of the two statements makes it circular. Take for example the following proof: 1. P→((P→P)→P) [axiom 1] 2. P→(P→P) [axiom 1] 3. (P→((P→P)→P))→((P→...

Therein lies your problem. You used the term "morally permissible" morals are like the tide, always a'changing. How can you base a logical, mathematical statement on such a shaky foundation? And your argument is not contradictory, but logically true, based on it's own definitions. Still c...

It's circular, because your topic says "Why people ought to be rational?" And you prove it by saying, being logical, is the most logical choice. No, what I have said is that any rational justification for the normative statement "irrationality is morally permissible" leads to a ...

Hi GreatandWiseTrixie, thank you for your reply, People hold on to delusion because it feels good, because they are taught what good is and that they should feel good and not bad. As well as their own instincts too, people like quick and easy. I understand that this must be an intuitive position to ...

I have constructed an argument defending the following proposition: people ought to act rationally. The purpose of this post is really to test it; please read it carefully, and be as critical as possible, for I should like to improve it if necessary and, in the event that any particularly devastatin...

One thing egg3000, could you point me towards or name this type of axiomatic proof as I've never encountered this kind before and would like to read-up. From what I see its using what I presume are tautologies(haven't checked yet) and one of the ND rules plus substitution to make deductive proofs? ...

I agree, the notion that humans are just these completely malleable blobs which are moulded entirely by experience is trivially false. Take the human visual system, for example: it is a biological system, and it therefore has certain scope and limitations. The average human retina, for example, cont...

So I posted the same problem elsewhere and a user named Melanie Turner responded with a solution. Here's the proof, I've edited it slightly, but only in order to make the notation more consistent with the previous posts in this thread—everything else is untouched. Axioms: P1. a → (b → a) P2. (a → (b...

I'm interested in this as I'd either forgotten or not understood it the first time, are you saying that if there is a valuation in a truth table that makes a proposition true but its not a tautology then Natural Deduction cannot prove it? Natural deduction is a different kind of proof method to the...