“One of these grand defects, as I humbly conceive, is this, that children are habituated to learning without understanding.”

From Italian: La filosofia è scritta in questo grandissimo libro, che continuamente ci sta aperto innanzi agli occhi (io dico l'Universo), ma non si può intendere, se prima non il sapere a intender la lingua, e conoscer i caratteri ne quali è scritto. Egli è scritto in lingua matematica, e i caratteri son triangoli, cerchi ed altre figure geometriche, senza i quali mezzi è impossibile intenderne umanamente parola; senza questi è un aggirarsi vanamente per un oscuro labirinto.
Other translations:
Philosophy is written in that great book which ever lies before our eyes — I mean the universe — but we cannot understand it if we do not first learn the language and grasp the symbols, in which it is written. This book is written in the mathematical language, and the symbols are triangles, circles and other geometrical figures, without whose help it is impossible to comprehend a single word of it; without which one wanders in vain through a dark labyrinth.
The Assayer (1623), as translated by Thomas Salusbury (1661), p. 178, as quoted in The Metaphysical Foundations of Modern Science (2003) by Edwin Arthur Burtt, p. 75.
Philosophy is written in this grand book — I mean the universe — which stands continually open to our gaze, but it cannot be understood unless one first learns to comprehend the language in which it is written. It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures, without which it is humanly impossible to understand a single word of it; without these, one is wandering about in a dark labyrinth.
As translated in The Philosophy of the Sixteenth and Seventeenth Centuries (1966) by Richard Henry Popkin, p. 65
Il Saggiatore (1623)
Source: Galilei, Galileo. Il Saggiatore: Nel Quale Con Bilancia Efquifita E Giufta Si Ponderano Le Cofe Contenute Nellalibra Astronomica E Filosofica Di Lotario Sarsi Sigensano, Scritto in Forma Di Lettera All'Illustr. Et Rever. Mons. D. Virginio Cesarini. In Roma: G. Mascardi, 1623. Google Play. Google. Web. 22 Dec. 2015. <https://play.google.com/store/books/details?id=-U0ZAAAAYAAJ>.

Source: Ulysses

During an interview by Lesley Stahl on 60 Minutes https://www.youtube.com/watch?v=1R42mFx3_ss (17 July 2016)
2010s, 2016, July

The Second Part, Chapter 27, p. 152
Leviathan (1651)

The Language and Thought of the Child (1923) Tr. Marjorie and Ruth Gabain (1926)
Context: If children fail to understand one another, it is because they think they understand one another. The explainer believes from the start that the reproducer will grasp everything, will almost know beforehand all that should be known, and will interpret every subtlety. Children are perpetually surrounded by adults who not only know much more than they do, but who also do everything in their power to understand them, who even anticipate their thoughts and desires. Children, therefore... are perpetually under the impression that people can read their thoughts, and in extreme cases, can steal their thoughts away. It is obviously owing to this mentality that children do not take the trouble to express themselves clearly... This mentality does not contradict ego-centric mentality. Both arise from the belief of the child, the belief that he is the centre of the universe. These habits of thought account... for the remarkable lack of precision in the childish style.

"Postscript to the News", broadcast on BBC radio, June 5, 1940; published in The Listener, June 13, 1940.

On his journey as an actor in “Edward James Olmos Reflects on the Legacy of ‘Stand and Deliver,’ Three Decades Later” https://remezcla.com/features/film/edward-james-olmos-stand-and-deliver-30-years/ in Remezcla (2019 May 30)

"Betrayals", p. 1; first published in Blue Motel (1994)
Four Ways to Forgiveness (1995)

Source: 1920s, Sceptical Essays (1928), Ch. 14: Freedom Versus Authority in Education