[Intellectual courage is] the quality that allows one to believe in one's judgement in the face of disappointment and widespread skepticism. Intellectual courage is even rarer than physical courage.

A good deal of scepticism in a scientific man is advisable to avoid much loss of time, for I have met with not a few men, who, I feel sure, have often thus been deterred from experiment or observations, which would have proved directly or indirectly serviceable.

An extremely healthy dose of skepticism about the reliability of science is an absolutely inevitable consequence of any scientific study of its track record.

As for Lindbergh, another eminent servant of science, all he proved by his gaudy flight across the Atlantic was that God takes care of those who have been so fortunate as to come into the world foolish.
Expressing skepticism that adventure does not necessarily contribute to scientific knowledge.

As immoral and unethical as this may be [to clone a human], there is a real chance that could have had some success. This is a pure numbers game. If they have devoted enough resources and they had access to enough eggs, there is a distinct possibility. But, again, without any scientific data, one has to be extremely skeptical.
Commenting on the announcement of the purported birth of the first cloned human.

Every scientist is an agent of cultural change. He may not be a champion of change; he may even resist it, as scholars of the past resisted the new truths of historical geology, biological evolution, unitary chemistry, and non-Euclidean geometry. But to the extent that he is a true professional, the scientist is inescapably an agent of change. His tools are the instruments of change—skepticism, the challenge to establish authority, criticism, rationality, and individuality.

Few men speak humbly of humility, chastely of chastity, skeptically of skepticism.

If mankind is to profit freely from the small and sporadic crop of the heroically gifted it produces, it will have to cultivate the delicate art of handling ideas. Psychology is now able to tell us with reasonable assurance that the most influential obstacle to freedom of thought and to new ideas is fear; and fear which can with inimitable art disguise itself as caution, or sanity, or reasoned skepticism, or on occasion even as courage.

In a lot of scientists, the ratio of wonder to skepticism declines in time. That may be connected with the fact that in some fields—mathematics, physics, some others—the great discoveries are almost entirely made by youngsters.

In mathematics, … and in natural philosophy since mathematics was applied to it, we see the noblest instance of the force of the human mind, and of the sublime heights to which it may rise by cultivation. An acquaintance with such sciences naturally leads us to think well of our faculties, and to indulge sanguine expectations concerning the improvement of other parts of knowledge. To this I may add, that, as mathematical and physical truths are perfectly uninteresting in their consequences, the understanding readily yields its assent to the evidence which is presented to it; and in this way may be expected to acquire the habit of trusting to its own conclusions, which will contribute to fortify it against the weaknesses of scepticism, in the more interesting inquiries after moral truth in which it may afterwards engage.

It is the tension between creativity and skepticism that has produced the stunning and unexpected findings of science.

It must, however, be confessed that this species of scepticism, when more moderate, may be understood in a very reasonable sense, and is a necessary preparative to the study of philosophy by preserving a proper impartiality in our judgments and weaning our mind from all those prejudices which we may have imbibed from education or rash opinion.

Most institutions demand unqualified faith; but the institution of science makes skepticism a virtue.

Science requires an almost complete openness to all ideas. On the other hand, it requires the most rigorous and uncompromising skepticism.

Scientists tend to be skeptical, but the weakness of the community of science is that it tends to move into preformed establishment modes that say this is the only way of doing science, the only valid view.

Skepticism and debate are always welcome and are critically important to the advancement of science, [but] skepticism that fails to account for evidence is no virtue.

Skepticism enables us to distinguish fancy from fact, to test our speculations.

Skepticism is a useful tool of the inquisitive mind, but it is scarcely a method of investigation.

Some ideas are better than others. The machinery for distinguishing them is an essential tool in dealing with the world and especially in dealing with the future. And it is precisely the mix of these two modes of thought [skeptical scrutiny and openness to new ideas] that is central to the success of science.

The Greeks made Space the subject-matter of a science of supreme simplicity and certainty. Out of it grew, in the mind of classical antiquity, the idea of pure science. Geometry became one of the most powerful expressions of that sovereignty of the intellect that inspired the thought of those times. At a later epoch, when the intellectual despotism of the Church, which had been maintained through the Middle Ages, had crumbled, and a wave of scepticism threatened to sweep away all that had seemed most fixed, those who believed in Truth clung to Geometry as to a rock, and it was the highest ideal of every scientist to carry on his science “more geometrico.”

The hype, skepticism and bewilderment associated with the Internet—concerns about new forms of crime, adjustments in social mores, and redefinition of business practices— mirror the hopes, fears, and misunderstandings inspired by the telegraph. Indeed, they are only to be expected. They are the direct consequences of human nature, rather than technology.
Given a new invention, there will always be some people who see only its potential to do good, while others see new opportunities to commit crime or make money. We can expect the same reactions to whatever new inventions appear in the twenty-first century.
Such reactions are amplified by what might be termed chronocentricity—the egotism that one’s own generation is poised on the very cusp of history. Today, we are repeatedly told that we are in the midst of a communications revolution. But the electric telegraph was, in many ways, far more disconcerting for the inhabitants of the time than today’s advances are for us. If any generation has the right to claim that it bore the full bewildering, world-shrinking brunt of such a revolution, it is not us—it is our nineteenth- century forebears.

The institutional goal of science is the extension of certified knowledge. The technical methods employed toward this end provide the relevant definition of knowledge: empirically confirmed and logically consistent predictions. The institutional imperatives (mores) derive from the goal and the methods. The entire structure of technical and moral norms implements the final objective. The technical norm of empirical evidence, adequate, valid and reliable, is a prerequisite for sustained true prediction; the technical norm of logical consistency, a prerequisite for systematic and valid prediction. The mores of science possess a methodologic rationale but they are binding, not only because they are procedurally efficient, but because they are believed right and good. They are moral as well as technical prescriptions. Four sets of institutional imperatives–universalism, communism, disinterestedness, organized scepticism–comprise the ethos of modern science.

The method of science is tried and true. It is not perfect, it’s just the best we have. And to abandon it, with its skeptical protocols, is the pathway to a dark age.

The origin of what we call civilization is not due to religion but to skepticism. … The modern world is the child of doubt and inquiry, as the ancient world was the child of fear and faith.

The Religion that is afraid of science dishonours God and commits suicide. It acknowledges that it is not equal to the whole of truth, that it legislates, tyrannizes over a village of God's empires but is not the immutable universal law. Every influx of atheism, of skepticism is thus made useful as a mercury pill assaulting and removing a diseased religion and making way for truth.

The scientist explores the world of phenomena by successive approximations. He knows that his data are not precise and that his theories must always be tested. It is quite natural that he tends to develop healthy skepticism, suspended judgment, and disciplined imagination.

The virtues of science are skepticism and independence of thought.

There are science teachers who actually claim that they teach “a healthy skepticism.” They do not. They teach a profound gullibility, and their dupes, trained not to think for themselves, will swallow any egregious rot, provided it is dressed up with long words and an affectation of objectivity to make it sound scientific.

Too much openness and you accept every notion, idea, and hypothesis—which is tantamount to knowing nothing. Too much skepticism—especially rejection of new ideas before they are adequately tested—and you're not only unpleasantly grumpy, but also closed to the advance of science. A judicious mix is what we need.

When I was a boy, I read with great interest but skepticism about a magic lamp which was used with success by a certain Aladdin. Today I have no skepticism whatsoever about the magic of the xenon flash lamp which we use so effectively for many purposes.

Young men, have confidence in those powerful and safe methods, of which we do not yet know all the secrets. And, whatever your career may be, do not let yourselves become tainted by a deprecating and barren skepticism … Live … until the time comes when you have the immense happiness of thinking that you have contributed in some way to the progress and to the good of humanity.