It seems the ultimate riddle: How could One God be Three Persons? How could One be Three? Or Three be One? And why three? Non-believers and believers can both enjoy the logic and linguistics.
The Trinity – A Philosophical Inquiry
Peter van Inwagen
Peter van Inwagen works in metaphysics, philosophy of action (free will), philosophy of...
Michael Rea works in philosophy of religion, analytic theology, metaphysics, feminist...
Brian Leftow works in philosophical theology, especially the nature and necessity of God