Re: [math-fun] Logic question

On 2/1/2017 6:19 PM, David Wilson wrote:

Can a reductio ad adsurdum argument be rearranged into a direct argument that does not require a supposition?

As well as any logical argument. Any logical argument proceeds from premises and shows they entail a conclusion. Whether the premises are suppositions or facts is not relevant to the logic. An argument from absurdity is of the form X=>Y, Y is absurd and therefore false, not-Y => not-X ... which seems direct to me. Do you just mean you want it to prove a positive? in which case you can substitute Z = not-X so it becomes not-Z=>Y, Y is absurd and therefore false, not-Y=>Z. Brent Meeker

In short, are suppositions necessary for logical arguments?