“If I say that there cannot be more than one consciousness in the same mind, this seems a blunt tautology — we are quite unable to imagine the contrary…”

Lecture, Scientology and Effective Knowledge (15 July 1957).

Source: The Varieties of Religious Experience

Original French: Il est donc tout simplement faux que ce dont on ne peut parler (au sens ou il n'y a rien à en dire qui le spécifie, qui lui accorde des propriétés séparatrices), il faille le taire. Il faut au contraire le nommer...
From Manifesto for Philosophy. Albany: State University of New York Press, 1999. ISBN 0791442209.
The quote is a commentary on Ludwig Wittgenstein, "Whereof one cannot speak, thereof one must be silent".

Interview with Suzie Daggett at Insight: Healthy Living (July 2006).
Context: Mystics, contrary to religionists, are always saying that reality is not two things — God and the world — but one thing, consciousness. It is a monistic view of reality based on consciousness that mystics claim to directly intuit. The problem with science has always been that most scientists believe that science must be done within a different monistic framework, one based on the primacy of matter. And then, quantum physics showed us that we must change that myopic prejudice of scientists, otherwise we cannot comprehend quantum physics. So now we have science within consciousness, a new paradigm of science based on the primacy of consciousness that is gradually replacing the old materialist science. Why? Not only because you can't understand quantum physics without this new metaphysics but also because the new paradigm resolves many other paradoxes of the old paradigm and explains much anomalous data.

Source: The Summing Up (1938), p. 164

Alles ist einfacher, als man denken kann, zugleich verschränkter, als zu begreifen ist.
Maxim 1209, trans. Stopp
Variant translation: Everything is simpler than we can imagine, at the same time more complex and intertwined than can be comprehended.
Maxims and Reflections (1833)

As quoted in "Terry Gilliam reflects to Dreams about the making of Dr Parnassus" by Phil Stubbs http://www.smart.co.uk/dreams/parntgrf.htm
Context: We read Dover Books, because you can steal from them. The medieval imagery and iconography is so good for the imagination. Trying to describe the world, trying to describe the cosmos, trying to put it down in neat orderly fashion, unlike reality. And it always seems to stick in one's mind more than reality does.

Discourses and Mathematical Demonstrations Relating to Two New Sciences (1638); Discorsi e dimostrazioni matematiche, intorno à due nuove scienze, as translated by Henry Crew and Alfonso de Salvio (1914)
Other quotes
Source: Discorsi E Dimostrazioni Matematiche: Intorno a Due Nuoue Scienze, Attenenti Alla Mecanica & I Movimenti Locali