It is commonly said that all synthetic propositions are subject to doubt, but is this really the case?

It is commonly said that all synthetic propositions are subject to doubt, but is this really the case? For example, is there any logical reason to doubt that humans are intelligent organisms that live on a planet called earth?

I don't know just who it is you mean who holds that. But, in general, it seems to me that although all propositions of any kind are subject to doubt, no proposition ought to be doubted unless there is a good reason for doubting it. Doubting is not, after all, one of the rights of man. And neither (I suggest) does doubting simply consist in uttering the words, "I hereby doubt that P" perhaps accompanied by some sensation of hesitancy.

I think the answer is that my doubting means I do not believe. But I am not convinced yet.

I think a spectrum view of belief/doubt is more accurate than a binary view. Would you agree that doubt and certainty are largely emotional?

I think a spectrum view of belief/doubt is more accurate than a binary view. Would you agree that doubt and certainty are largely emotional?

But, in general, it seems to me that although all propositions of any kind are subject to doubt, no proposition ought to be doubted unless there is a good reason for doubting it.

Sure. But then one must decide what constitutes a good reason.

I do not know much about the formation of belief or doubt, so I can't really answer that. I would suspect that emotion does play a role in our formation of belief, but to what extent I do not know. I don't think it's entirely an issue of emotion, though; we often believe things for good reasons, and emotion never comes into the picture.

Of course. But, a lot of the time, that's quite easy. For instance, if you are at a magic show, and someone is suppose to be cutting a woman in half, you have excellent reason to doubt he is. Or, if someone is known to be a congenital liar, and he tells you the Moon is made of cream cheese, you have excellent reason to doubt what he says. See what I mean?

If only it were always that easy....but it's not.

It is commonly said that all synthetic propositions are subject to doubt, but is this really the case? For example, is there any logical reason to doubt that humans are intelligent organisms that live on a planet called earth?

Of course it is reasonable of us to conclude that this is not the case, but the point is it is always open to philosophical doubt.

Well no, but just because this is the most logical conclusion to come to about the world given the evidence - Russell calls the external world a 'working hypothesis' - does not mean its the right one.
It would be logical for someone who had never experienced water before to assume it would not impede their breathing, just as it is logical for me to conclude that I am alive and I live on planet earth, because I have no reason to believe otherwise. But both are dubitable, there is always the chance that tomorrow I will wake up on another planet and find out I was part of some sort of Matrix like experiment.

Of course it is reasonable of us to conclude that this is not the case, but the point is it is always open to philosophical doubt.

But what kind of doubt is philosophical doubt? The American pragmatist, Charles Peirce called it, "sham doubt" , "fake doubt", and "paper doubt", since it has no connection to action. We can philosophically doubt there is a chair at the same time we try to sit on it. Peirce wrote, "We ought not to doubt in philosophy what we do not doubt in our hearts".

Oh you have to read the Peirce quote on my page, its beautiful...

You have a point, and Peirce does have a way with words, but, like Reconstructo says, this is only one point on our 'spectrum of truth', the truth which we use daily, the truth which we have to have to make us human and not just abstractions. But we cannot forget the rest of the spectrum because in it, somewhere, lies absolute truth, and this is what philosophy was born to find.
What i mean by philosophical truth is that truth men have been searching for for centuries, the one Descartes thought he had found when i said 'cogito ergo sum', the one indubitable proposition upon which everything else, morality, spirituality, reality, can be built; the fulcrum with which we can move the world.
No, its not practical, and, no, the search for it may only lead us on pathways of pure abstraction, but it is still truth, in its purest form, undiluted by our humanity, our 'being' - without which we are not, and yet somehow we are something so much more than what we are - and we cannot forget that, no matter how incomprehensible it can become.

I can understand why you might want to believe that. But I don't understand why you do believe it. I mean your reasons. Ponce de Leon was always wanting to find The Fountain of Youth. I can understand why, but I don't understand why he believed there was such a thing as The Fountain of Youth.

Because if there isn't absolute truth, then there isn't any truth at all, in which case we're both mistaken

Because if there isn't absolute truth, then there isn't any truth at all, in which case we're both mistaken