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To begin with, I know that if I need X , does not necessarily mean that X exists.

But in some cases, it seems very convincing that if I need X then X exists. These are some examples :

  • If I am hungry (i.e need food) then food exists
  • If I am thirsty then water exists

Although, I do not see this as conclusive evidence, or at least a valid reasoning ... Since, the apparent reasoning in these statements may well be due to the fact that there is some inductive reasoning operating in the background, thus :

  • It is not that If I am hungry then food exists , but it is more like : If I take food then I won't be hungry based on previous experience, which implies (of necessity) that food exists.

So, in this case : the fact that I am hungry does not, per se, imply that food exists, by virtue of a direct link or necessity between "I need food" and "food exists".

But by virtue of previous particulars where I ate food and it did well with hunger , so it must be that food exists, because : I ate food implies it, because the inductive generalization implies it.

Otherwise, if I am wrong, is there a name for the evidence from need? is it even reasonable to say (in all or some cases) that If I need X then X exists? is it valid reasoning?

Any references will be very appreciated.

Note It is obvious that this reasoning does not seem valid, if I need a time machine to go back and change my past, it does not necessarily mean that time machines exist. , But what I am asking about, is only the apparently valid cases like I need water, I need food..etc.

Thanks

  • 1
    Maybe this is somewhat relevant... The theme/sort of reasoning kind of reminds me of one of CS Lewis's arguments for God/afterlife. According to Wikipedia, Lewis's argument is called the argument from desire. – Adam Sharpe Aug 2 at 16:39
  • @AdamSharpe Thank you for the reference, yes I heard about the argument from desire, which can be considered as an appeal to emotion. Although the example here is about whether there is a link/necessity, or at least implication between "I need food" and "food exists" ... or is it a false implication? – SmootQ Aug 2 at 16:42
  • I don't understand why you think that "If I eat food I won't be hungry" implies "there is food". If there is no more food in the world the former is still true, but the latter false. – Eliran Aug 2 at 16:59
  • @Eliran , by implies here I mean "induction" ... this is the inductive argument : P1 : I ate food many times in the past to stop hunger ", P2 "It worked" , Conclusion : "If I eat food then I won't be hungery" . But this inductive argument presumes that there was something that is called "food" in the past (not necessarily in the future). That is : the idea of "food" matched some state of affairs in the actual world. So it implies that "food" exist(ed) – SmootQ Aug 2 at 17:24
  • But then why not cut the 'hungry' part out of the argument and just say I know that food exists because I've eaten some in the past? – Bumble Aug 2 at 18:34
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Here are dictionary definitions of the term "imply" as used in the context of logical arguments:

"To involve by logical necessity".

Or

"to suggest or involve as a necessary consequence".

Being hungry obviously doesn't imply that food exists.

It might, at least in principle, if you could at all include in the premises of your argument the entirety of the scientific explanation of the sensation of hunger.

And then, this might at best only prove that food has existed, not that it exists now.

The necessary formal expression of the scientific explanation itself probably doesn't even exist yet. It is much simpler and faster and more convincing to rely on our belief that food exists somewhere, and accept the natural sensation of hunger as proof enough that food... doesn't exist at least in our own stomach.

It is also possible to have the sensation of hunger with a full belly.

Note 1 There is no "inductive implication" in the sense you use here. Inductive implication is a particular method of proof used in mathematics, with only a vague relation of similarity to inductive logic.

In inductive logic, conclusions are never necessarily true. They are merely conceivably true and reasonable to accept as long as they are not falsified by empirical evidence.

Note 2 It is also unclear, and therefore definitely not any deductive implication, whether what we take to be the sensation of hunger itself necessarily implies a need for food.

There is no deductively logical reason that I could think of that this sensation might not also be experienced by some alien species somewhere in the universe, or indeed outside of it, but then signalling a completely different need, like a need for sleep or something, or indeed any functionally operational "mood", i.e. something of significance to these aliens in the context of their individual or collective life.

  • thank you ! "this might at best only prove that food has existed, not that it exists now." , I do not mean that food exists now, but that food exists as an actual idea (regardless of the time it existed). And I agree that induction does not lead to a "necessarily true conclusion" but only very probable one. Thanks again ! +1 – SmootQ Aug 2 at 21:43
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The confusion here comes from assumptions that are perhaps implicit in the statement, but not explicitly spelled out. We need to break down exactly what is meant by I need water. What is missing here is why you need water. The complete statement here is obviously, "I need water to live". Or even more precisely, "I need x liters of water every t seconds to live". Now that we've explicitly spelled out what we're saying, we can reason about it properly.

"If I need (and have always needed) x liters of water every t seconds to live, and I've been alive for more than t seconds, then at least x liters of water must have existed at some point in the past" is valid. It is also likely, based on what we empirically know about how water works, that at least that much water still exists, but that doesn't necessarily follow logically. Even then, we can easily construct a situation where it doesn't follow, especially if we change "water" to "water I can access": just place me in a space capsule with only a finite amount of water, and at some point, toss it out the airlock. I still need accessible water to live, but there isn't any left.

What is valid empirical reasoning is, "If I am thirsty, and cease to be thirsty when I drink water, then not only does water exist now, but it probably also existed when humans first evolved." But the fact that we need it in the present doesn't imply that it will always exist in the future. There have been many situations where a species needs something to live, and that thing ceases to exist (at least in sufficient quantities). The result of such situations isn't contradiction, but rather extinction. And during the last moments before extinction, the species and the need still exist, but the necessary resource does not.

  • Thank you @Ray +1 ..! I agree with the statement "But the fact that we need it in the present doesn't imply that it will always exist in the future. " .. I do not mean by "exist" that it exists now or in the future, I only mean that the idea of food / water exists in the actual world regardless of the time it existed. Since we evolved and we need water to survive, it means that water existed along our evolutionary history. I Couldn't agree more ! – SmootQ Aug 2 at 21:47

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