Because of the importance of philosophy to the University's curriculum throughout much of its history, the Library has a strong collection in this field. The precise size of the collection is hard to determine since it has evolved over many decades and is shelved according to several classification schemes. The Library aims to acquire all standard critical editions and current works in both the historical and systematic areas of philosophy. The Special Collections Department includes approximately 600 Aristotle and pseudo-Aristotelian texts and commentaries written before 1750, both published and manuscript. The Lea Library is strong in late medieval and Renaissance philosophy. The Yarnall Collection is strong in medieval philosophy and theology. The Schrecker Collection, acquired in 1963, contains 5000 volumes on the history of modern philosophy from Descartes to Hegel, with special emphasis on Leibniz. The Library currently maintains subscriptions to over 115 philosophy journals.
The philosophy collection is substantially complemented by those of the hard and life sciences (philosophy of science, bioethics, philosophy of mind), literature (continental philosophy), Biddle law library (philosophy of law), and Lippincott Library (business ethics). Likewise, the collection related to non-western philosophy is complemented by Area Studies collections.