Re: An argument against modus ponens

John Jones wrote:
The significance of "if" statements is that they allow for at least two possibilities- that something (P) is the case, or not the case (R). Our disagreement falls on the description of 'not the case', or 'absent' as I describe it below.

1) Firstly, both cases need a syntactical representation if we are to retain the grammatical significance of 'if' statements.

2) Let's argue against me: 'If P' entails either only P or the absence of P, but does not entail R. However, I argue that in this case, the absence of P entails the absence of the context of P.

Explanation: If the absence of P did not entail the absence of the context of P, and the context of P is retained, then the absence of P must be represented in that context. For example, if P is a physical object and if we retain the context of physical objects, then the absence of P is a vacuum (R), or a lost or hidden object (R), or some such (R). But if P is a physical object and if both P AND its context is absent, then there are no physical objects, period. This would say more than we intended about the specifications laid out by our 'if P ..' statement, and undermine 1) above (undermine the scenario laid out by if statements). More importantly, we cannot represent the two outcomes - P being the case or not the case, if only P has a context.

Are you arguing against abstraction itself? I ask because in this reply you seem to switch suddenly from talking about logical or abstract relationships to talking about concrete "contexts," without signalling that you're doing so, and without justifying it. As soon as you say, "for example, if P is a physical object" I think, huh? Where'd he get the idea that P could be a physical object?

I think your (R) is just the same as "not P." If you're making a point about the nature of abstraction, please say so. Can you explain what you mean by "context" without using any philosophical jargon? I think that would really advance the ball.







.

Relevant Pages

  • Re: An argument against modus ponens
    ... So "if P" requires the consideration of another element or object through which a truth value may be ascertained. ... 'If P' entails either only P or the absence of P, but does not entail R. However, I argue that in this case, the absence of P entails the absence of the context of P. ... If the absence of P did not entail the absence of the context of P, and the context of P is retained, then the absence of P must be represented in that context. ... For example, if P is a physical object and if we retain the context of physical objects, then the absence of P is a vacuum, or a lost or hidden object, or some such. ...
    (sci.logic)
  • Re: An argument against modus ponens
    ... 'If P' entails either only P or the absence of P, but does not entail R. However, I argue that in this case, the absence of P entails the absence of the context of P. ... If the absence of P did not entail the absence of the context of P, and the context of P is retained, then the absence of P must be represented in that context. ... For example, if P is a physical object and if we retain the context of physical objects, then the absence of P is a vacuum, or a lost or hidden object, or some such. ...
    (sci.logic)
  • Re: Imbedding a JPEG image in a MSWord document using APL
    ... old and sore to reinvent any wheels:)) ... In the absence of any more details about the context of your question the code below will create an instance of Word using APL+WIN and insert a jpg image file. ...
    (comp.lang.apl)
  • Re: Lack of evidence does not constitute proof of nonexistence
    ... good evidence of absence, depending upon the context. ... It is, I agree, very hard to prove the absolute non-existence of something. ...
    (soc.history.ancient)