Complex sentence: In one case, though, it is claimed that Schopenhauer raised a very important criticism: his objection to Kant's assertion that a particular event can be known as being successive only if its particular cause is known.
Split into simpler sentences: In one case, though, it is claimed that Schopenhauer raised a very important criticism. That is his objection to Kant's assertion that a particular event can be known as being successive only if its particular cause is known.