“What is then your idea of the progress of Science? Science advances one step, then another, and then draws back and meditates before taking a third. Does the impossibility of taking that last step suppress the success acquired by the two others? Would you say to an infant who hesitated before a third step, having ventured on two previous ones; ‘Thy former efforts are of no avail; never shalt thou walk’? “You wish to upset what you call my theory, apparently in order to defend another; allow me to tell you by what signs these theories are recognized: the characteristic of erroneous theories is the impossibility of ever foreseeing new facts; whenever such a fact is discovered, those theories have to be grafted with further hypotheses in order to account for them. True theories, on the contrary, are the expression of actual facts and are characterized by being able to predict new facts, a natural consequence of those already known. In a word, the characteristic of a true theory is its fruitfulness.” “Science,” said he again at the following sitting of the Academy, “should not concern itself in any way with the philosophical consequences of its discoveries. If through the development of my experimental studies I come to demonstrate that matter can organize itself of its own accord into a cell or into a living being, I would come here to proclaim it with the legitimate pride of an inventor conscious of having made a great discovery, and I would add, if provoked to do so, ‘All the worse for those whose doctrines or systems do not fit in with the truth of the natural facts.’ “It was with similar pride that I defied my opponents to contradict me when I said, ‘In the present state of science the doctrine of spontaneous generation is a chimera.’ And I add, with similar independence, ‘All the worse for those whose philosophical or political ideas are hindered by my studies.’ “This is not to be taken to mean that, in my beliefs and in the conduct of my life, I only take account of acquired science: if I would, I could not do so, for I should then have to strip myself of a part of myself. There are two men in each one of us: the scientist, he who starts with a clear field and desires to rise to the knowledge of Nature through observation, experimentation and reasoning, and the man of sentiment, the man of belief, the man who mourns his dead children, and who cannot, alas, prove that he will see them again, but who believes that he will, and lives in that hope, the man who will not die like a vibrio, but who feels that the force that is within him cannot die. The two domains are distinct, and woe to him who tries to let them trespass on each other in the so imperfect state of human knowledge.”