By no amount of reasoning can we altogether eliminate all contingency from our world. Moreover, pure speculation alone will not enable us to get a determinate picture of the existing world. We must eliminate some of the conflicting possibilities, and this can be brought about only by experiment and observation.

Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe? The usual approach of science of constructing a mathematical model cannot answer the questions of why there should be a universe for the model to describe. Why does the universe go to all the bother of existing?

I am too much of a sceptic to deny the possibility of anything.

I doubt that Fleming could have obtained a grant for the discovery of penicillin on that basis [a requirement for highly detailed research plans] because he could not have said, 'I propose to have an accident in a culture so that it will be spoiled by a mould falling on it, and I propose to recognize the possibility of extracting an antibiotic from this mould.'

Philosophy stands in need of a science which shall determine the possibility, principles, and extent of human knowledge à priori.

Scientific reasoning is a kind of dialogue between the possible and the actual, between what might be and what is in fact the case.

The major religions on the Earth contradict each other left and right. You can't all be correct. And what if all of you are wrong? It's a possibility, you know. You must care about the truth, right? Well, the way to winnow through all the differing contentions is to be skeptical. I'm not any more skeptical about your religious beliefs than I am about every new scientific idea I hear about. But in my line of work, they're called hypotheses, not inspiration and not revelation.

The truth us that other systems of geometry are possible, yet after all, these other systems are not spaces but other methods of space measurements. There is one space only, though we may conceive of many different manifolds, which are contrivances or ideal constructions invented for the purpose of determining space.

What [man landing on the moon] is doing up there is indulging his obsession with the impossible. The impossible infuriates and tantalizes him. Show him an impossible job and he will reduce it to a possibility so trite that eventually it bores him.

Where any answer is possible, all answers are meaningless.
[Referring to speculations (on 'Not as We Know It' alien lifeforms) made in the total absence of evidence.]

Where the untrained eye will see nothing but mire and dirt, Science will often reveal exquisite possibilities.