“Rational, adj. Devoid of all delusions save those of observation, experience and reflection.”

Source: Predestination? On Why God Made Those Who Would Perish

No. 15
On the Interpretation of Nature (1753)
Context: There are three principal means of acquiring knowledge available to us: observation of nature, reflection, and experimentation. Observation collects facts; reflection combines them; experimentation verifies the result of that combination. Our observation of nature must be diligent, our reflection profound, and our experiments exact. We rarely see these three means combined; and for this reason, creative geniuses are not common.

Source: Seven Great Statesmen in the Warfare of Humanity with Unreason (1915), p. 167

No. 71
The Federalist Papers (1787–1788)

Source: What Is This Thing Called Science? (Third Edition; 1999), Chapter 1, Science as knowledge derived form the facts of experience, p. 8.

Lady Slings the Booze (1992)

Heinz von Foerster cited in: Bernhard Poerksen (2004). The Certainty of Uncertainty: Dialogues Introducing Constructivism. p.3
2000s and attributed from posthumous publications

Source: Moral Man and Immoral Society (1932), p.221
Context: The naïve faith of the proletarian is the faith of the man of action. Rationality belongs to the cool observers. There is of course an element of illusion in the faith of the proletarian, as there is in all faith. But it is a necessary illusion, without which some truth is obscured. The inertia of society is so stubborn that no one will move against it, if he cannot believe that it can be more easily overcome than is actually the case.