Audience: readers who have completed the process thinking lesson.
Learning goal: explain what actual occasions are and how prehension works as the basic relational act.
If reality is fundamentally processual, what are the basic units of process? Whitehead’s answer is the actual occasion: a momentary event of experience that constitutes itself through its relations to prior occasions and then perishes, contributing its achieved character to what comes after.
An actual occasion is not a substance — not a simple, self-identical thing that persists through time. It happens once and is done. Its identity is not given in advance but achieved through the process of becoming. What an occasion is depends entirely on what it prehends — what it grasps from the occasions in its past — and how it integrates those prehensions. An occasion apart from its prehensions is nothing; the prehensions are constitutive.
Prehension is the key concept. The word is chosen to avoid the connotations of “perception” — prehension is not necessarily conscious, not limited to organisms, and not primarily cognitive. Every actual occasion prehends the occasions in its past. An electron interaction prehends prior electron states. A molecular event prehends the molecular occasions around it. Prehension is the basic relational act of the universe.
Prehension has three components: the prehending subject (the occasion in process), the datum (what is prehended), and the subjective form (how the datum is received — with what valuation, emphasis, or exclusion). There are also negative prehensions: an occasion can exclude a datum from its integration, and this exclusion is itself a constitutive act.
Whitehead distinguishes physical prehensions (grasping the actualized data of prior occasions) from conceptual prehensions (grasping eternal objects — possibilities — that shape how the data is valued). Both kinds enter into every occasion’s self-constitution.
The result is a picture where relations are genuinely prior to relata. The occasion is not a thing that then prehends; it is a prehending that achieves thingness. This is relational ontology expressed in the most rigorous terms Western philosophy has produced.
Check for understanding: Why does Whitehead use the word “prehension” instead of “perception”?