For he was grounded in astronomye.
He kepte his pacient a ful greet deel
In houres by his magyk natureel.
Wel koude he fortunen the ascendent
Of his ymages for his pacient.
– Geoffrey Chaucer
The Canterbury Tales, General Prologue. The Physician is instructed in astronomy and uses natural science and the study of astrological signs to help treat his patients. He knows how to calculate the planetary position to improve the state of his patient.