“Archibald: To understand this, it is not necessary to think of anything at all.
Saphir: Let us think of nothing at all!”
Patience (1881)
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W. S. Gilbert 67
English librettist of the Gilbert & Sullivan duo 1836–1911Related quotes

To Army War College Graduates, Carlisle Barracks, Pennsylvania, 7 June 2008 http://www.jcs.mil/chairman/speeches/07JUN08_ArmyWarCollege_Commencement.html, CJCS.

“But as to all opinions which do not strike at the root of Christianity, we think and let think.”
"The Character of a Methodist" (1739); in The Works of the Rev. John Wesley in Ten Volumes (1826), Volume IV, p. 407; A portion of this is commonly quoted as "Think and let think.".
General sources
Context: The distinguishing marks of a Methodist are not his opinions of any sort. His assenting to this or that scheme of Religion, his embracing any particular set of notions, his espousing the judgment of one man or of another, are all quite wide of the point. Whosoever therefore imagines, that a Methodist is a man of such or such an opinion, is grossly ignorant of the whole affair; he mistakes the truth totally. We believe indeed, that all Scripture is given by the inspiration of God, and herein we are distinguished from Jews, Turks, and Infidels. We believe the written word of God to be the only and sufficient rule, both of Christian faith and practice; and herein we are fundamentally distinguished from those of the Romish church. We believe Christ to be the eternal, supreme God; and herein we are distinguished from the Socinians and Arians. But as to all opinions which do not strike at the root of Christianity, we think and let think. So that whatsoever they are, whether right or wrong, they are no distinguishing marks of a; Methodist.

Source: Church leaders hail Philippine peace deal http://www.archivioradiovaticana.va/storico/2017/04/07/church_leaders_hail_philippine_peace_deal/en-1304176 (2017)

“They who think they know all, learn nothing.”
Source: Aphorisms and Reflections (1901), p. 257