1. Leibniz’s reformulation of the Ontological Argument
Gottfried Leibniz ( ).
Key text: Philosophical Papers and Letters.
Rationalist.
Sought to demonstrate that God’s necessary existence, as a concept, contained no contradictions and thus is logically possible.

2. Leibniz’s reformulation of the Ontological Argument
Leibniz attempted to fill what he thought was a shortcoming in Descartes’ version of the OA.
Descartes had argued that a “clear and distinct” idea of God entailed his existence.
Leibniz’ argument focused instead on the logical possibility of God’s necessary existence.

3. Leibniz’s reformulation of the Ontological Argument
Leibniz claimed that Descartes’ arguments fail unless one first shows that the idea of a supremely perfect being is coherent.
He set himself the task of proving that there is no contradiction within the concept of a supremely perfect being.
“ …we cannot safely infer from definitions until we know that they are real or that they involve no contradiction.”

4. Leibniz’s reformulation of the Ontological Argument
The ‘principle of non-contradiction’: a concept is valid, possible, true and real if it does not contain contradictions.
Maintained that concepts of perfection were possible and that they were simple, unanalysable and compatible.
“ I call every simple quality which is positive and absolute, or expresses whatever it expresses without any limits, a perfection.”

5. Leibniz’s reformulation of the Ontological Argument
All can be drawn together with a single possible concept of supreme perfection.
“ …it is not difficult to show that all perfections are compatible with each other or can exist in the same subject.”
For the statement “there is a perfect being” to be contradictory two of the perfections must be incompatible.
As perfections are simple, positive and absolute this situation cannot arise.

6. Leibniz’s reformulation of the Ontological Argument
Argued that existence was a perfection and that supreme perfection would entail infinite existence.
Therefore a perfect being or God exists.
Often remarks that the OA itself demonstrates only that if it is possible that God exists then God exists.
If this is correct then a proof of ‘It is possible that God exists’ would quite literally be required to complete the ontological argument.