**Tags**

accident, Active Intellect, Avicenna, immaterial, immutable, intelligibles, matter, mind, necessity, substance, truth, Tusi

Tusi wrote a compact treatise on establishing the existence of a being separate from matter that is the ground of the truth of our necessary judgments. Here’s my summary of his argument:

A necessary truth is one whose truth-value can’t change. Now, where *p* (= belief, judgment, proposition, statement) is necessarily *true*, concede this: *p* is true iff *p* corresponds to something.

This something then, call it *x*, to which *p* corresponds, either exists (1) outside the mind or (2) it doesn’t. If (2), it follows that *p** (where *p** is a *false* judgment, belief, proposition, statement) is true; for *p** also has something corresponding to it in the mind. But that’s a contradiction. Therefore, *x* exists outside the mind.

As external to the mind, *x* is either (1.1) self-subsistent or (1.2) inheres in another being. If (1.1), *x* is either (1.1.1) spatio-temporally located or (1.1.2) not. If (1.1.1), *p* would not be, contra what was assumed, *necessarily* true. But that’s a contradiction. If (1.1.2), *x* would be a Platonic Form. But there are no such entities. Therefore, (1.2) *x* inheres in another being outside the mind.

This other being *x* inheres in is itself either (1.2.1) spatio-temporally located or (1.2.2) not. If (1.2.1), *x* would inherent its spatio-temporal condition; *p* would then, again, not be necessarily true – a contradiction. Therefore, (1.2.1) *x* inheres in another being that is not spatio-temporally located.