Mi dicevo che è vano sperare, per Atene e per Roma, quell'eternità che non è accordata né gli uomini né alle cose, e che i più saggi tra noi negano persino agli dèi. [...] La natura ci tradisce, la fortuna muta, un dio dall'alto guarda ogni cosa. [...]
M. Yourcenar, Memorie di Adriano
L’incertezza necessaria per apprezzare la natura non è facilmente correlabile alla sensazione di certezza di fede che di solito è associata a una profonda convinzione religiosa.
R. Feynman
Abduction and induction have, to be sure, this common feature, that both lead to the acceptance of a hypothesis because observed facts are such as would necessarily or probably result as consequences of that hypothesis. But for all that, they are the opposite poles of reason, the one the most ineffective, the other the most effective of arguments. The method of either is the very reverse of the other’s. Abduction makes its start from the facts, without, at the outset, having any particular theory in view, though it is motived by the feeling that a theory is needed to explain the surprising facts. Induction makes its start from a hypothesis which seems to recommend itself, without at the outset having any particular facts in view, though it feels the need of facts to support the theory. Abduction seeks a theory. Induction seeks for facts. In abduction, the consideration of the facts suggests the hypothesis. In induction, the study of the hypothesis suggests the experiments which bring to light the very facts to which the hypothesis had pointed. The mode of suggestion by which, in abduction, the facts suggest the hypothesis is by resemblance,—the resemblance of the facts to the consequences of the hypothesis. The mode of suggestion by which in induction the hypothesis suggests the facts is by contiguity,—familiar knowledge that the conditions of the hypothesis can be realized in certain experimental ways.
