Origins
The word 'ontological' is built from the most fundamental verb in any language — 'to be' — and applied to the most fundamental question philosophy can ask: what exists? Greek 'on' (ὄν), the present participle of 'einai' (εἶναι, to be), means 'being' or 'that which is.' The genitive form 'ontos' (ὄντος) gives the combining form 'onto-,' and when joined with '-logia' (study of, from 'logos,' word/reason), it produces 'ontologia' — the study of being itself.
The Proto-Indo-European root *h₁es- (to be) behind Greek 'einai' is perhaps the most essential verb ever reconstructed. Its descendants include English 'is,' 'am,' and 'are' (through Germanic *isti, *izmi); Latin 'esse' (to be), which produced 'essence,' 'entity,' 'absent,' 'present,' and 'interest'; Sanskrit 'asti' (he is); Old Church Slavonic 'jesti' (is); and Hittite 'eszi' (is). Every branch of the Indo-European family preserves this root, testifying to its irreducible importance in human thought and language.
The word 'ontologia' was coined in the early seventeenth century by scholars who felt that existing philosophical vocabulary was inadequate to name what they were doing. Aristotle had called it 'first philosophy' or 'the study of being qua being' (to on hē on) — the investigation of what it means for anything to exist, prior to asking what particular things exist. But Aristotle had no single-word name for this inquiry. The coinage 'ontologia' filled the gap, and it was independently proposed by several philosophers, including Rudolf Goclenius (1613) and Christian Wolff (1730).
Development
The most famous ontological concept in philosophy is the ontological argument for the existence of God, first formulated by Anselm of Canterbury in the eleventh century. Anselm argued that God, defined as 'that than which nothing greater can be conceived,' must exist in reality as well as in the mind, because existing in reality is greater than existing only in the mind. This argument — which attempts to prove God's existence from the mere concept of God, without any empirical evidence — has fascinated and infuriated philosophers for a millennium. Kant's devastating objection — that 'existence is not a predicate,' that saying something exists adds nothing to the concept of that thing — remains the standard philosophical response, though the argument continues to be reformulated and debated.
In the twentieth century, ontology experienced a renaissance through the work of Martin Heidegger, who made the 'question of Being' (Seinsfrage) the central concern of his philosophy. Heidegger argued that Western philosophy had forgotten the question of Being — had busied itself with particular beings (entities, objects, facts) while neglecting the fundamental question of what it means for anything to be at all. His masterwork 'Being and Time' (1927) attempted to reopen this question through an analysis of human existence (Dasein), which he regarded as the kind of being that is uniquely capable of asking about Being.
In analytic philosophy, ontology took a different direction. W.V.O. Quine framed the ontological question as: 'What is there?' — and answered with his famous criterion: 'To be is to be the value of a variable.' In other words, we are committed to the existence of whatever entities our best scientific theories require us to quantify over. This approach transformed ontology from a speculative inquiry into a technical exercise in logical analysis.
Modern Usage
In contemporary usage, 'ontological' has spread beyond professional philosophy into information science ('ontology' as a formal specification of a conceptual framework), computer science (knowledge representation systems), and popular intellectual discourse. An 'ontological question' in everyday usage is any question about what fundamentally exists or what category something belongs to — 'Is consciousness a physical process?' 'Are nations real entities or useful fictions?' 'Does the number seven exist?'
The word's power lies in its direct connection to the verb 'to be.' Every time someone says 'ontological,' they are invoking the deepest stratum of language and thought — the simple, unanswerable question embedded in the most common verb in any human tongue: what does it mean to be?