The individual substances, of which the universe is composed, fall into three great irreducible kinds: nature, God, man.
There remains too the consequence that there are different substances, separate from but related to one another; and these substances of three irreducible kinds, natural, supernatural, human.
On British railways the duty of the companies to provide all practicable safeguards and to educate and caution the servants may be said to have been faithfully performed, and the accident totals must be taken as being somewhat near the " irreducible minimum" - unless some of the infirmities of the human mind can be cured.
But if it is an error to treat the unity of the world as its only real aspect, it is equally an error to treat its differences as something ultimately irreducible.
It may be said summarily that Kant holds the antithesis between thought and " the given " to be unresolved and within the limits of theory of knowledge irreducible.