Process philosophy (or ontology of becoming) identifies metaphysical reality with change and development. Since the time of Plato and Aristotle, philosophers have posited true reality as "timeless", based on permanent substances, while processes are denied or subordinated to timeless substances. If Socrates changes, becoming sick, Socrates is still the same (the substance of Socrates being the same), and change (his sickness) only glides over his substance: change is accidental, whereas the substance is essential. Therefore, classic ontology denies any full reality to change, which is conceived as only accidental and not essential. This classical ontology is what made knowledge and a theory of knowledge possible, as it was thought that a science of something in becoming was an impossible feat to achieve.
In opposition to the classical model of change as accidental (as by Aristotle) or illusory, process philosophy regards change as the cornerstone of reality — the cornerstone of the Being thought as Becoming. Modern philosophers who appeal to process rather than substance include Nietzsche, Heidegger, Charles Peirce, Alfred North Whitehead, Alan Watts, Robert M. Pirsig, Charles Hartshorne, Arran Gare and Nicholas Rescher. In physics Ilya Prigogine distinguishes between the "physics of being" and the "physics of becoming". Process philosophy covers not just scientific intuitions and experiences, but can be used as a conceptual bridge to facilitate discussions among religion, philosophy, and science.
- In Ancient Greek thought
An early expression of this viewpoint is in Heraclitus's fragments. He posits strife, ἡ ἔρις (strife, conflict), as the underlying basis of all reality defined by change. The balance and opposition in strife were the foundations of change and stability in the flux of existence.
- Twentieth century
In early twentieth century philosophy of mathematics, it was undertaken to develop mathematics as an airtight axiomatic system, in which every truth could be derived logically from a set of axioms. In the foundations of mathematics, this project is variously understood as logicism or as part of the formalist program of David Hilbert. Alfred North Whitehead and Bertrand Russell attempted to complete, or at least greatly facilitate, this program with their seminal book Principia Mathematica, which purported to build a logically consistent set theory on which to found mathematics. After this, Whitehead extended his interest to natural science, which needs a deeper philosophical basis. He intuited that natural science was struggling to overcome a traditional ontology of timeless material substances, because it does not suit natural phenomena. They are more properly understood as 'process'. This resulted in the most famous work of process philosophy, Alfred North Whitehead's Process and Reality, 1929, a work which continues that begun by Hegel but describing a more complex and fluid dynamic ontology.
Process thought describes truth as "movement" in and through determinates (Hegelian truth), rather than describing these determinates as fixed concepts or "things" (Aristotelian truth). Since Whitehead, process thought is distinguished from Hegel in that it describes entities which arise or coalesce in becoming, rather than being simply dialectically determined from prior posited determinates. These entities are referred to as complexes of occasions of experience. It is also distinguished in being not necessarily conflictual or oppositional in operation. Process may be integrative, destructive or both together, allowing for aspects of interdependence, influence, and confluence, and addressing coherence in universal as well as particular developments, which aspects are not condign to Hegel's system. Additionally, instances of determinate occasions of experience, while always ephemeral, are nonetheless seen as important to define the type and continuity of those occasions of experience that flow from or relate to them.