Philosophy is of two kinds: natural and divine. Natural philosophy seeks knowledge of physical verities and explains material phenomena, whereas divine philosophy deals with ideal verities and phenomena of the spirit. The field and scope of natural philosophy have been greatly enlarged, and its accomplishments are most praiseworthy, for it has served humanity. But according to the evidence of present world conditions divine philosophy—which has for its object the sublimation of human nature, spiritual advancement, heavenly guidance for the development of the human race, attainment to the breaths of the Holy Spirit and knowledge of the verities of God—has been outdistanced and neglected. Now is the time for us to make an effort and enable it to advance apace with the philosophy of material investigation so that awakening of the ideal virtues may progress equally with the unfoldment of the natural powers. In the same proportion that the body of man is developing, the spirit of man must be strengthened; and just as his outer perceptions have been quickened, his inner intellectual powers must be sensitized so that he need not rely wholly upon tradition and human precedent. In divine questions we must not depend entirely upon the heritage of tradition and former human experience; nay, rather, we must exercise reason, analyze and logically examine the facts presented so that confidence will be inspired and faith attained. Then and then only the reality of things will be revealed to us. The philosophers of Greece—such as Aristotle, Socrates, Plato and others—were devoted to the investigation of both natural and spiritual phenomena. In their schools of teaching they discoursed upon the world of nature as well as the supernatural world. Today the philosophy and logic of Aristotle are known throughout the world. Because they were interested in both natural and divine philosophy, furthering the development of the physical world of mankind as well as the intellectual, they rendered praiseworthy service to humanity. This was the reason of the triumph and survival of their teachings and principles. Man should continue both these lines of research and investigation so that all the human virtues, outer and inner, may become possible.
(‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 326-327)

Strange indeed that after twenty years training in colleges and universities man should reach such a station wherein he will deny the existence of the ideal or that which is not perceptible to the senses. Have you ever stopped to think that the animal already has graduated from such a university? Have you ever realized that the cow is already a professor emeritus of that university? For the cow without hard labor and study is already a philosopher of the superlative degree in the school of nature. The cow denies everything that is not tangible, saying, “I can see! I can eat! Therefore, I believe only in that which is tangible!” Then why should we go to the colleges? Let us go to the cow.
(‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 360)

The animal can neither recognize nor apprehend the spiritual power of man and makes no distinction between man and itself, for the reason that its susceptibilities are limited to the plane of the senses. It lives under the bondage of nature and nature’s laws. All the animals are materialists. They are deniers of God and without realization of a transcendent power in the universe. They have no knowledge of the divine Prophets and Holy Books—mere captives of nature and the sense world. In reality they are like the great philosophers of this day who are not in touch with God and the Holy Spirit—deniers of the Prophets, ignorant of spiritual susceptibilities, deprived of the heavenly bounties and without belief in the supernatural power. The animal lives this kind of life blissfully and untroubled, whereas the material philosophers labor and study for ten or twenty years in schools and colleges, denying God, the Holy Spirit and divine inspirations. The animal is even a greater philosopher, for it attains the ability to do this without labor and study. For instance, the cow denies God and the Holy Spirit, knows nothing of divine inspirations, heavenly bounties or spiritual emotions and is a stranger to the world of hearts. Like the philosophers, the cow is a captive of nature and knows nothing beyond the range of the senses. The philosophers, however, glory in this, saying, “We are not captives of superstitions; we have implicit faith in the impressions of the senses and know nothing beyond the realm of nature, which contains and covers everything.” But the cow, without study or proficiency in the sciences, modestly and quietly views life from the same standpoint, living in harmony with nature’s laws in the utmost dignity and nobility.
(‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 311-312)