A mind is accustomed to mathematical deduction, when confronted with the faulty foundations of astrology, resists a long, long time, like an obstinate mule, until compelled by beating and curses to put its foot into that dirty puddle.
Interpretation
The quote illustrates the resistance of rational thought to accept unscientific beliefs, using a vivid metaphor of a stubborn mule.
Johannes Kepler's quote highlights the struggle of logical reasoning when faced with irrational concepts like astrology. He compares the mind to a mule that, despite its nature to resist, must ultimately confront and engage with flawed ideas, suggesting that scientific inquiry strives to confront and dispel such falsehoods, albeit with difficulty.
In practice
In a debate about the validity of astrology, you might use this quote to emphasize the importance of scientific reasoning.
...Those laws are within the grasp of the human mind. God wanted us to recognize them by creating us after his own image so that we could share in his own thoughts... and if piety allow us to say so, our understanding is in this respect of the same kind as the divine, at least as far as we are able to grasp something of it in our mortal life.
A most unfailing experience... of the excitement of sublunary (that is, human) natures by the conjunctions and aspects of the planets has instructed and compelled my unwilling belief.
We find, therefore, under this orderly arrangement, a wonderful symmetry in the universe, and a definite relation of harmony in the motion and magnitude of the orbs, of a kind that is not possible to obtain in any other way.
I am stealing the golden vessels of the Egyptians to build a tabernacle to my God from them, far far away from the boundaries of Egypt. If you forgive me, I shall rejoice; if you are enraged with me, I shall bear it. See, I cast the die, and I write the book. Whether it is to be read by the people of the present or of the future makes no difference: let it await its reader for a hundred years, if God himself has stood ready for six thousand years for one to study him.
Eyesight should learn from reason.
I measured the skies, now the shadows I measure, Sky-bound was the mind, earth-bound the body rests. [Kepler's epitaph]
That we can now think of no mechanism for astrology is relevant but unconvincing. No mechanism was known, for example, for continental drift when it was proposed by Wegener. Nevertheless, we see that Wegener was right, and those who objected on the grounds of unavailable mechanism were wrong.
How many more years I shall be able to work on the problem I do not know; I hope, as long as I live. There can be no thought of finishing, for 'aiming at the stars' both literally and figuratively, is a problem to occupy generations, so that no matter how much progress one makes, there is always the thrill of just beginning.
I don't think that science is complete at all. We don't understand everything, and one can see, within science itself, there are many inconsistencies. We just have to accept that we don't understand.
There is a single light of science, and to brighten it anywhere is to brighten it everywhere.
As history proves abundantly, mathematical achievement, whatever its intrinsic worth, is the most enduring of all.
It was like a new world opened to me, the world of science, which I was at last permitted to know in all liberty.
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