Before going into the details about my interpretation of the Five Ways text, I want to lay out some of the hermeneutical principles that guide my interpretation.
First, it is essential not to rely on English translations of Thomas’s works, or of the works of Aristotle, Maimonides, Avicenna, and other relevant thinkers. As Dan Bonevac and I have discovered over the last couple of years, the standard translations of the relevant works are highly unreliable. They are often paraphrases rather than translations, reflecting the translators assumption about what Thomas or Aristotle “must” mean by their words.
Second, the principle of charity must be foremost. We don’t believe that there is a single instance in the corpus of either Thomas or Aristotle in which either makes an elementary mistake of logic, and yet many interpreters attributes such errors to them with remarkable frequency. It is not hard to “find” an invalid or unpersuasive argument in a text. What is difficult is finding an excellent, and that should always be our goal. The argument we attribute to Thomas should not only be valid, it should rely only on premises that are plausible in themselves, reasonable to accept as first principles, and consistent with the other commitments that Thomas makes.
Third, we should not assume that anything in the Five Ways depends on the specific scientific theories and explanations that were accepted by Aristotle and by natural scientists in Thomas’s day. Thomas will occasionally make reference to such theories (for example, the theory of the four elements) in the first Part of the Summa, but these are always best taken as illustrations of Thomas’s meaning, not as evidence for the truth of what he is claiming. Thomas is quite aware of the fact that all such scientific hypotheses are uncertain at best, and probably false. We should distinguish between Aristotle’s metaphysics and fundamental philosophy of nature, on the one hand, and the various speculative theories and models that he employs, on the other. The latter have largely been discredited, but the former remain quite plausible.
Fourth, we should certainly take into account other passages in Thomas’s corpus that seem to be parallel with one or other of the Five Ways, but we should not assume that the Five Ways are merely a compressed allusion to those other passages. Where one of the Ways is much simpler and sparser than a parallel passage in, for example, the Summa Contra Gentiles, we should take seriously the possibility that the simplification and reduction is deliberate and significant, rather than an artifact of compression.
The Analytic Thomist 
All this is very nice, but wait a minute: who said that “Nihil est in intellectu, quod prius non fuerit in sensu”? Metaphysical concepts of matter and motion must be abstracted from sensual concepts of matter and motion – there is no other way. In the macroscopic world available to Aristotle and Thomas, motion seems to be something separate from matter, and hence the necessity of accepting the First Mover. However, examination of the microscopic world revealed that matter and motion are a dual unity, which makes an external Mover unnecessary.
What remains intact, however, is Thomas’s interpretation of the Prime Being as a pure act of existence. “If there is no existence in the beginning, then there is no existence at all” (Gabriel Marcel). Modern science allows us to conclude that the dual unity of “dynamis” and “energeia” pervades contingent being at all levels, and that the Prime Being is the tri-unity of “on (existence)”, “dynamis” and “energeia”. Thanks to this, what was previously a mystery of faith became available for purely discursive cognition. Isn’t that a beautiful prospect for combining Thomism with modern science, Rob?
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