Allow me to begin, the argument for the unmoved mover runs as follows:
No potentially existent state can be realized without a causal agent/ mechanism actually existing
No thing can simultaneously be in a state of actuality while in a state of potentiality in the same respect
4. therefore, things that change require something else to change them
This sequence of motion cannot extend ad infinitum
Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.
Let me to unpack this argument premise by premise. The first premise seems commonsensical. In our everyday experience we notice change in all different types. Aquinas had an Aristotelian view of change. Aristotle held that change was a reduction from potency to act. Potency, is a state that could potentially be but is not already, whereas act is a state that is already in act, or in action (existence). For instance, when we notice a block of marble, that block of marble is potentially a statue. In that case, the block of marble ITSELF exists in a state of potentiality with regards to being a statue. Potentiality is not a separate state of being that exists apart from the object being changed and is only achieved once that object has been changed, but rather, potentiality is a component of a being that could potentially be other than what it actually (currently) is. So, in the case of the block of marble, it currently exists in a state of potentiality with regards to being a statue given that it is not already a statue. Therefore, the block of marble is a composite of potentiality and actuality. Actuality is the state of being when a thing imposes its existence on the actual state of affairs, and not a merely possible (potential) state of affairs. So, when the block of marble’s potentiality for being a statue is realized and it actually becomes a statue then in that case the statue no longer exists in a state of potentiality, but rather, in a state of actuality. allow me to clarify something, a thing is potential insofar as that potentiality corresponds to that thing’s nature (acorns do not become butterflies, and caterpillars do not become trees). Aristotle’s definition of change may seem a little esoteric to some, however, Aristotle’s definition of change comes from a dilemma that was prevalent in his day. The dilemma was introduced by Parmenides, who argued that when a thing changes it gains attributes that it did not have before it changed, however, Parmenides took issue with the process of change in general. Parmenides argued that if change actually occurs then when a thing changes, the attributes that it gains either come from a nonexistent realm, or from an existent realm. If the the attributes gained during the process of change come from an existent realm, Parmenides argues, then the thing