Kalb argues that for Aquinas, a substance subsists because of its internal metaphysical design (its form and essence), which then allows it to receive esse. Gilson’s "existential Thomism" collapses subsistence into existence, erasing the structural foundation of Aristotle's metaphysics and leaving behind an unstable philosophy where essences are just empty names. [1, 2, 3]

Jeffrey C. Kalb Jr.’s critique focuses entirely on restoring the Aristotelian foundation of "substance" (substantia) and "subsistence" (subsistentia) in Thomas Aquinas, which he argues Étienne Gilson severely distorted. [1]

To understand Kalb's alternative reading, it helps to contrast how he and Gilson treat the internal structure of a created being.

1. The Core Dispute: What Makes a Substance Real?

In traditional metaphysics, a finite thing (like a horse or a human) is a substance—a primary existent that exists in itself, not in another. [1, 2, 3]

• The Gilsonian View: Gilson argued that a substance's essence is entirely inert and purely potential until it is "struck" by the act of existence (esse). For Gilson, the reality and individuality of a substance flow almost entirely from its existential act (esse), which acts as the supreme driver of reality. [1]
• The Kalb Critique: Kalb argues that Gilson treats essence as a completely blank, passive void. In doing so, Gilson implicitly turns the concrete substance into a mere byproduct of an external act of existence, which strips the substance of its inherent, stable reality. [1]

Gilson's Model:  [ Esse (Act of Being) ]  ======>  [ Passive Essence ]  =  Existent Being
Kalb's Model:    [ Subsistence (Essence + Form) ] <--> [ Esse (Act of Being) ] = Complete Substance

2. Kalb’s Key Reinterpretation: Essence as Active Form

Kalb contends that Aquinas never intended for esse to swallow up the reality of essence. Instead, Kalb emphasizes that a material substance's essence already contains an intrinsic principle of actuality: substantial form. [1, 2]

• Kalb points out that in texts like De Ente et Essentia (On Being and Essence), Aquinas explicitly states that the essence of a natural substance includes both matter and form. [1]
• Form is what gives a substance its specific, intelligible boundaries and active power. By ignoring the robust reality of substantial form, Gilson acts as if an essence has no intelligibility of its own before receiving esse—a step Kalb claims veers directly into semi-nominalism. [1]

3. The Distinction Between Esse and Subsistentia

The title of Kalb's work, Existence and Subsistence, highlights his central linguistic and metaphysical correction of Gilson. He argues that Gilson conflated two distinct concepts in Aquinas's Latin: [1]

1. Existence (Esse): The actual state of being real, which is shared by everything that exists.
2. Subsistence (Subsistentia): The internal structural capacity of a specific nature to hold itself together and exist independently. [1, 2, 3]

Kalb argues that for Aquinas, a substance subsists because of its internal metaphysical design (its form and essence), which then allows it to receive esse. Gilson’s "existential Thomism" collapses subsistence into existence, erasing the structural foundation of Aristotle's metaphysics and leaving behind an unstable philosophy where essences are just empty names. [1, 2, 3]