Full Idea
Demonstrations are probative deductions [sullogismos] which give the explanation [aitias] and the reason why.
Clarification
'Probative' means providing proof
Gist of Idea
Demonstrations are syllogisms which give explanations
Source
Aristotle (Posterior Analytics [c.327 BCE], 85b24)
Book Reference
Aristotle: 'Posterior Analytics (2nd ed)', ed/tr. Barnes,Jonathan [OUP 1993], p.37
A Reaction
This notion seems to have slipped out of modern philosophy of science, because (while scientists have just pressed on) philosophers of science have raised so many sceptical questions that they have, I would say, lost the plot.