Not that a posteriori is denied, or that idealism even in Hegel tries to evolve reality out of the philosopher's inner consciousness.
Again, these contrasted philosophies throw light upon the meaning of a posteriori and a priori in Kant and subsequent writers.
He differs, however, from Kant, not only because he will not allow that the given data are received from things in themselves, but also because, like Mach, he agrees with the nativists that the data already contain a spatial determinacy and a temporal determinacy, which he regards as a posteriori elements of the given, not like Kant, as a priori forms of sense.
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Anselm was not thoroughly satisfied with this reasoning; it started from a posteriori grounds, and contained several converging lines of proof.
So long as the relation of the nominal to the real essence has no other background than Locke's doctrine of perception, the conclusion that what Kant afterwards calls analytical judgments a priori and synthetic judgments a posteriori exhaust the field follows inevitably, with its corollary, which Locke himself has the courage to draw, that the natural sciences are in strictness impossible.
Kant's analysis of knowledge had disclosed the a priori element as the necessary complement of the isolated a posteriori facts of experience.
The existence of God is maintained by Albert and Aquinas to be domonstrable by reason; but here again they reject the ontological argument of Anselm, and restrict themselves to the a posteriori proof, rising after the manner of Aristotle from that which is prior for us to that which is prior by nature or in itself.
Cleanthes and Philo come to an agreement, in admitting a certain illogical force in the a posteriori argument, or, at least, in expressing a conviction as to God's existence, which may not perhaps be altogether devoid of foundation.
Avenarius (q.v.) is the hypothesis of the inseparability of subject and object, or, to use his own phraseology, of ego and environment, in purely empirical, or a posteriori form.
Finally, side by side with a theory of the nature of moral obligation thus fundamentally empirical and a posteriori in its outlook, he maintains in his account of justice the existence of the idea of justice as distinct from a mere sentiment, carrying with it an a priori belief in its existence and identical in its a priori and intuitive character with the ultimate criterion of Utilitarianism itself.