Caption: Immanuel Kant (1724--1804), German philosopher, scientist, and theoretical astronomer, in a portrait showing a lot of craquelure.

Features:

1. In the context of Newtonian physics, the nebular hypothesis of Solar System formation was first fully proposed by Kant---who is more famous as a philosopher than as an astronomer. The proposal was in his book Universal Natural History and Theory of the Heavens (1755). Some parts were proposed by earlier in 1734 by Emanuel Swedenborg (1688--1772): Kant was familiar with this work (see Wikipedia: Nebular hypothesis: History; Wikipedia: History of Solar System formation and evolution hypotheses: Formation hypothesis).

2. An important aspect of Kant's nebular hypothesis and of his cosmological cosmological theory (see below) was that they emphasized historical change in the universe rather than an changeless universe created at some instant or eternal which was the common view of European natural philosophers in the 18th century (see Stephen Toulmin (1922--2009), The Discovery of Time, 1965, p. 101, 125, 132--135). Note Kant's theories qualitative. He was NO mathematical astronomer.

3. Kant was also the second to propose that the Milky Way was a disk of the stars sustained against collapse to a single object by rotational motion (i.e., angular momentum) just as the Solar System is so sustained. The first for Milky Way speculation was Thomas Wright (1711--1786) (see Wikipedia: Thomas Wright: Astronomy) whose book Kant had seen a review of. The third was Johann Heinrich Lambert (1728--1777) who claimed to have come to his speculations NOT knowing of those of Wright and Kant. See No-404--407.

   Wright (probably independently) was also the second to speculate that nebulae (or some of them) were other galaxies outside of the Milky Way (see Wikipedia: Thomas Wright: Astronomy). Kant was the third to so speculate (probably NOT independently) (see Wikipedia: Immanuel Kant: Early Work; Stephen Toulmin (1922--2009), The Discovery of Time, 1965, p. 131) and Lambert the fourth (perhaps independently).

4. About the nebulae as other galaxies, who was first? None other than architect Christopher Wren (1632--1723) (see christopher_wren.html). But Wren's speculation seems to have had NO historical impact---but it is a credit to his genius.

5. Another of Kant's claims to fame is as the proposer of the categorical imperative as the foundation of morality/ethics:
   Act so that the maxim (determining motive of the will) may be capable of becoming a universal law for all rational beings.

   And yet another is Kant's definition of the enlightenment applicable to The Enlightenment:

   Enlightenment is man's emergence from self-imposed immaturity. Immaturity is the inability to use one's understanding without guidance from another. This immaturity is self-imposed when its cause lies NOT in lack of understanding, but in lack of resolve and courage to use without guidance from another. Sapere aude (dare to know)! "Have the courage to use you own understanding!"---that is the motto of enlightenment.
   ---Emmanuel Kant, Answering the Question: What is Enlightenment? (1784) quoted from H. Floris Cohen's (1946--) How Modern Science Came into the World: Four Civilizations, One 17th-Century Breakthrough (2011, p. 733).