“We do not know what things look like.
We know what things are like. It must be a very limiting thing, this seeing. -Aunt Beast”

Source: Tertium Organum (1912; 1922), Ch. I
Context: The most difficult thing is to know what we do know, and what we do not know.
Therefore, desiring to know anything, we shall before all else determine WHAT we accept as given, and WHAT as demanding definition and proof; that is, determine WHAT we know already, and WHAT we wish to know.
In relation to the knowledge of the world and of ourselves, the conditions would be ideal could we venture to accept nothing as given, and count all as demanding definition and proof. In other words, it would be best to assume that we know nothing, and make this our point of departure.
But unfortunately such conditions are impossible to create. Knowledge must start from some foundation, something must be recognized as known; otherwise we shall be obliged always to define one unknown by means of another.

How to Raise a Prodigy, The New Yorker (2018)

Book of Imaginary Beings (1957), as translated by Norman Thomas di Giovanni
Context: It is universally held that the unicorn is a supernatural being and of auspicious omen; so say the odes, the annals, the biographies of worthies, and other texts whose authority is unimpeachable. Even village women and children know that the unicorn is a lucky sign. But this animal does not figure among the barnyard animals, it is not always easy to come across, it does not lend itself to zoological classification. Nor is it like the horse or bull, the wolf or deer. In such circumstances we may be face to face with a unicorn and not know for sure that we are. We know that a certain animal with a mane is a horse and that a certain animal with horns is a bull. We do not know what the unicorn looks like.

The Stark Munro Letters (1894)

Source: Change of Heart

" Greek finance minister: 'I don't know if we did the right thing' http://www.theguardian.com/business/video/2015/jul/16/greek-bailout-finance-minister-vote-video" (16 July 2015)

Inaugural Address (1989)

[Norris, K., The Cloister Walk, Penguin Publishing Group, 1997, 978-1-101-21566-1, http://books.google.com/books?id=pZkLNwpYcJ0C&pg=PT115]