Most contemporary accounts of cosmological arguments assume that they rest on the principle of sufficient reason. Problematically, no Medieval or ancient philosopher ever mentioned such a principle, though they appear pretty cognizant of the principles they’re using. For St. Thomas, it’s clear that he is not appealing to a principle of sufficient reason but a principle of first cause. He comes right out and says it in the First Way – immediately after he argues omne quod movetur ab alio movetur he says
But this does not go on forever, because then there would not be some first moving thing, and per consequens no other moving thing, since secondary movers do not move except from the fact that they are moved by the first thing moving.
Hic autem non est procedere in infinitum, quia sic non esset aliquod primum movens; et per consequens nec aliquod aliud movens, quia moventia secunda non movent nisi per hoc quod sunt mota a primo movente.
It would be understandable to find the premise baffling, and even question begging – how can St. Thomas set down an axiom that all causal chains have some first?
The “first” in question here is the “per se and primo” (or Aristotle’s kath’auto and katholou). To explain: some causes are ordered effects per se or simply in virtue of what they are, but they are not what is first of all ordered to that effect. Can openers qua can openers (i.e. per se) are causally ordered to taking the lid off a can, but they are not first of all what is responsible for removing it – the first thing that does so is the agent who uses the tool. Though this example is taken from efficient causality, there are examples in all of the per se causes. Notice, however, that there is a pretty clear division between the first per se cause and the sufficient cause or reason. I’m the first cause of opening a can, but not the sufficient cause – without a tool, I don’t have much more of a chance than the tool has without me. Contrariwise, fire is a per se and sufficient cause of heat but it is not the first cause of heat – that’s mean molecular motion. And so not all first causes are sufficient causes or vice-versa.
The principle St. Thomas is working from is in fact more axiomatic and obvious than the principle of sufficient reasoning – since to be a first cause in the relevant sense just means to be what, in the last analysis, just is the cause. Among per se causes (if there is more than one) the “first” one is simply the one that is the most per se. If the axiom needs a name, call it the principle of primal causality.
Just Thomism 
Jarvis Claim said,
July 10, 2013 at 6:44 pm
I am interested in what you argue here. But what would you say to someone who says a contingent thing, i.e something that either can or cannot exist, may exist without a cause? This postulate is not a contradiction, so how would you prove absolutely it is false? Must you appeal to an axiomatic principle of sufficient reason or principle of causality? If so, what if someone says the principle is not self-evident? I look forward to hearing what you answer. Thanks in advance!
James Chastek said,
July 11, 2013 at 7:39 am
Both philosophy and modern science see the contingent as explained and caused by the necessary. If you want to explain some trait, you set about looking for something that has that trait necessarily. If you want to explain heat, for example, you start looking around for something that is hot of itself, i.e. necessarily hot. Fire, for example, might be the cause of every hot thing (maybe, as the ancients thought, fire was an element that could be mixed into things to make them hot) the hypothesis didn’t work out, but it was only replaced by something that cannot exist without being hot (a sort of molecular motion). Likewise, if you want to explain the stability of the earth, you can’t say that it rests on the back of a turtle, since turtles of themselves are not a fixed and solid ground. You either need an explanation like the earth resting at the center of the universe (since centers are fixed of themselves) or that all of its parts are moving along with it more or less inertially. Again, if you want to explain the cause of malaria, you need something that causes it of itself. You might initially think it was caused by humidity or getting ones feet wet and call it swamp fever, but you quickly realize this can’t cause it of itself. Later on, you might narrow down the cause to mosquitoes, but you aren’t done until you find something like protists, i.e. microorganisms that just are malaria or themselves.
Notice that the axiom at work here is that if there is some _______ it has to be explained and caused by what is ______ by itself. The thing in the blank is whatever you want to explain, and the “by itself” might be possessed by a single thing or a complex of things. Given that contingent things do not exist of themselves, then if existence is what you want to explain, you can’t appeal to what exists contingently – this would be the same sort of mistake as trying to explain the stability of the earth by resting it on the back of a turtle, or trying to explain AIDS by blaming it on gay sex. In this sense, the axiom is self-evident. If you want to explain colds by saying they are the effect of low temperatures, everyone can recognize there is something deficient in your explanation as soon as you notice that many people get colds when it is warm. Something else has to be at work.
It may seem here that I’m appealing to a principle of sufficient reason. PSR is fine as far as it goes, but the more fundamental principle of primal causality.
vetdoctor said,
July 11, 2013 at 8:26 pm
Quite good. It it’s common to see internet posts claiming quanta wink into existence without cause thus there is no need for a first cause. Since quanta were not and now are they cannot contain within themselves the cause of their existence.