Natural science in so far as it had to do with more or less verifiable data could not be considered harmful, and so we find Judah Halevi taking pains to show that the sages of Rabbinical literature cultivated the sciences, astronomy in connection with the Jewish calendar; anatomy, biology and physiology in relation to the laws of slaughter and the examination of animal meat (laws of "Terefa").[203] But so great was the fascination philosophy exerted upon the men of his generation that even Judah Halevi, despite his efforts to shake its authority and point out its inadequacy and evident inferiority to revelation, was not able wholly to escape it. And we find accordingly that he deems it necessary to devote a large part of the fifth book of the Kusari to the presentation of a bird's eye view of the current philosophy of the day. To be sure, he does not give all of it the stamp of his approval; he repeatedly attacks its foundations and lays bare their weakness. At the same time he admits that not every man has faith by nature and is proof against the erroneous arguments of heretics, astrologers, philosophers and others. The ordinary mortal is affected by them, and may even be misled for a time until he comes to see the truth. It is therefore well to know the principles of religion according to those who defend it by reason, and this involves a knowledge of science and theology. But we must not, he says, in the manner of the Karaites, advance all at once to the higher study of theology. One must first understand the fundamental principles of physics, psychology, and so on, such as matter and form, the elements, nature, Soul, Intellect, Divine Wisdom. Then we can proceed to the more properly theological matters, like the future world, Providence, and so on. Accordingly Judah Halevi gives us in the sequel a brief account such as he has just outlined. It will not be worth our while to reproduce it all here, as in the first place Judah Halevi does not give it as the result of his own investigation and conviction, and secondly a good deal of it is not new; and we have already met it in more or less similar form before in Joseph ibn Zaddik, Abraham bar Hiyyah, and others. We must point out, however, the new features which we did not meet before, explain their origin and in particular indicate Judah Halevi's criticisms.