Translation by Burtt, ibid., Vol. III. p. 156 
Secondary works, Joannis Kepleri Astronomi Opera Omnia (1858)
                                    
“Indeed I reply in a single word to the sentiments of the saints on these questions about nature; in theology, to be sure, the force of authorities is to be weighed, in philosophy, however, that of causes.”
            Therefore, a saint is Lactantius, who denied the rotundity of the earth; a saint is Augustine, who, admitting the rotundity, yet denied the antipodes; worthy of sainthood is the dutiful performance of moderns who, admitting the meagreness of the earth, yet deny its motion. But truth is more saintly for me, who demonstrate by philosophy, without violating my due respect for the doctors of the church, that the earth is both round and inhabited at the antipodes, and of the most despicable size, and finally is moved among the stars. 
Vol. III, p. 156 
Joannis Kepleri Astronomi Opera Omnia, ed. Christian Frisch (1858)
        
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Johannes Kepler 51
German mathematician, astronomer and astrologer 1571–1630Related quotes
Literary Essays, vol. II (1870–1890), Rousseau and the Sentimentalists
                                        
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                                        with A., Kushiner, James M., (editors),[2001, Signs of intelligence: understanding intelligent design, Brazos Press, Grand Rapids, Mich., 1587430045, [BL263.S54, 2001], 00067612] 
2000s
                                    
In response to a question about whether he writes differently for different audiences, in an Inteview at HarperCollins.com
The Origins of Knowledge and Imagination (1978)
                                        
                                        Third letter on sunspots (December 1612) to Mark Wesler (1558 - 1614), as quoted in Discoveries and Opinions of Galileo (1957) by Stillman Drake, p. 134 - 135; Italian text online at  Liber Liber http://www.liberliber.it/biblioteca/g/galilei/lettere/html/lett08c.htm, also from  IntraText http://www.intratext.com/IXT/ITA0188/_PQ.HTM.
Variant translation: In questions of science the authority of a thousand is not worth the humble reasoning of a single individual.
As quoted in Biographies of Distinguished Scientific Men (1859) by François Arago, as translated by Baden Powell, Robert Grant, and William Fairbairn, p. 365 
Other quotes 
Variant: In the sciences, the authority of thousands of opinions is not worth as much as one tiny spark of reason in an individual man. 
Context: for in the sciences the authority of thousands of opinions is not worth as much as one tiny spark of reason in an individual man. Besides, the modern observations deprive all former writers of any authority, since if they had seen what we see, they would have judged as we judge.