If I am requested to formulate the ground-principles of the philosophy of Mahayana Buddhism, and, indeed, of all the schools of Buddhism, I would suggest the foillowing:
(1) All is momentary.
(2) All is empty.
(3) All is without self.
(4) All is such as it is.
These four tenets, as it were, are so closely interrelated that, stand or fall, they all inevitably share one fate together.
--- from "Outlines of Mahayana Buddhism" by D.T. Suzuki