The correlation of science and ethics in Hermann Cohen's philosophy

Hermann Cohen made a distinction between the logic of science and the ideal of ethics, and noted that the natural world and the world of ethics are perceived very differently. This is because the order of the physical world is unchangeable (e.g, the sun sets in the west, night follows day, etc), while in the ideal world ethical rules can be accepted or rejected. It seems there should be one explanation for science, which is empirically self-evident, and another for ethics, which is something that is open to debate. Cohen reasoned there must be something that allows science and ethics to coexist and interrelate