Just as man goes forward, in the natural movement of his body, only by putting one foot in front of the other, so in the natural movement of his mind, man goes forward only by putting one idea in front of another. In other words, the mind, like the body, needs a primary point of support. The body's point of support is the ground which the foot feels; the mind's point of support is the known, that is, a truth or a principle of which the mind is aware. Man can learn nothing except by going from the known to the unknown; but on the other hand, as science is not infused into man at birth, and as he knows only what he learns, we seem to be in a vicious circle, where man is condemned to inability to learn anything. He would be so, in fact, if his reason did not include a feeling for relations and for determinism, which are the criteria of truth; but in no case can he gain this truth or approach it, except through reasoning and experience.
It would be incorrect to say that deduction pertains only to mathematics and induction to the other sciences exclusively. Both forms of reasoning, investigating (inductive) and demonstrating (deductive), pertain to all possible sciences, because in all the sciences there are things that we do not know and other things that we know or think we know.
When mathematicians study subjects unfamiliar to them, they use induction, like physicists, chemists or physiologists.