“When we believe that science or religion "has the truth," we stop our speculations. While still referring to the theory of evolution, science accepts it as a fact, about existence, and therefore any speculation that threatens that theory becomes almost heretical.”

“Hindu maxim that theory, speculations, [and] dogma change from time to time as the facts become better understood.”

“The greater the number of conjectured theories that are confronted by the realities of the world, and the more speculative those conjectures are, the greater will be the chances of major advances in science.”

“In the penultimate decade of the twentieth century science is sufficiently advanced to resolve the puzzles that stymied scientists in the last century and demonstrate, without metaphysical speculation, the consistency of evolution in all realms of experience. It is now possible to advance a general evolution theory based on unitary and mutually consistent concepts derived from the empirical sciences.”

“And this [experimental] science verifies all natural and man-made things in particular, and in their appropriate discipline, by the experimental perfection, not by arguments of the still purely speculative sciences, nor through the weak, and imperfect experiences of practical knowledge. And therefore, this is the matron of all preceding sciences, and the final end of all speculation.”
Et hæc scientia certificat omnia naturalia et artificialia in particulari et in propria disciplina, per experientiam perfectam; non per argumenta, ut scientiæ pure speculativae, nec per debiles et imperfecta experientias ut scientiae operativæ. Et ideo hæc est domina omnium scientiarum præcedentium, et finis totius speculationis.

“The Theory of Evolution, like the Theory of Gravity, is a scientific fact. Evolution really happened. Accepting our kinship with all life on earth is not only solid science, in my view, it's also a soaring spiritual experience. (From the second Cosmos: ASO episode, Some of the Things That Molecules Do.)”

“When we meet a fact which contradicts a prevailing theory, we must accept the fact and abandon the theory, even when the theory is supported by great names and generally accepted.”

“One important idea is that science is a means whereby learning is achieved, not by mere theoretical speculation on the one hand, nor by the undirected accumulation of practical facts on the other, but rather by a motivated iteration between theory and practice.”

“We wish to find the truth, no matter where it lies. But to find the truth we need imagination and skepticism both. We will not be afraid to speculate, but we will be careful to distinguish speculation from fact.”

“Darwinian evolution may be the most truthful and powerful idea ever generated by Western Science, but if we continue to illustrate our conviction with an indefensible, unsupported, entirely speculative, and basically rather silly story, then we are clothing a thing of beauty in rags - and we should be ashamed, "for the apparel oft proclaims the man."”