St. Thomas Aquinas
Proof ex motu of the Existence of God
Logical reconstruction by Jan Salamucha (1903-1944)


Latin text

  1. Certum est enim et sensu constat, aliqua moveri in hoc mundo.
  2. Omne autem quod movetur, ab alio movetur.
  3. Nihil enim movetur, nisi secundum quod est in potentia ad illud ad quod movetur:
  4. movet autem aliquid secundum quod est actu.
  5. Movere enim nihil aliud est quam educere aliquid de potentia in actum,
  6. de potentia autem non potest aliquid reduci in actum, nisi per aliquod ens in actu.
  7. Non autem est possibile ut idem sit simul in actu et potentia secundum idem...
  8. Impossibile est ergo quod, secundum idem et eodem modo, aliquid sit movens et motum, vel quod moveat seipsum
  9. omne ergo quod movetur, oportet ab alio moveri.
  10. Si ergo id a quo movetur, moveatur, oportet et ipsum ab alio moveri; et illud ab alio.
  11. Hic autem non est procedere in infinitum:
  12. quia sic non esset aliquod primum movens;
  13. et per consequens nec aliquod aliud movens,
  14. quia moventia secunda non movent nisi per hoc quo sunt mota a primo movente.
  15. Ergo necesse est devenire ad aliquod primum movens, quod a nullo movetur;
  16. et hoc omnes intelligunt Deum.


Logical reconstruction


Some clarifications

  1. "AC(x,y)" - "x is in actu with respect to y";
  2. "D(x)" - "x is God";
  3. "def" - "definition";
  4. "emp" - "empirical sentence";
  5. "M(x)" - "x is primum movens";
  6. "MAD(x,y,z)" - "x is moved by y with respect to z";
  7. "ont" - "ontological sentence";
  8. "PO(x,y)" - "x is in potentia with respect to y";
  9. "R* < Inf" - "created by R-row is unlimited";
  10. "mu(x)" - "x is in movement"


Simplifying of the proof in ordinary language (according to the Latin text)

(1) It is sure and empirically evident that some things in the world are being moved.
(2) But everything that is being moved is being moved by something other.
(10) If, therefore, that [entity] by which it is being moved should also be being moved, it [i.e., that entity] also must itself be in a state of being moved by another, and that [entity] by another [entity].
(11) But this [causal chain of entities potentially moving and being moved] is not in the [actual] state of going on to infinity.
(15) Therefore it is necessary to arrive at something first doing the moving, which is being moved by nothing else.
(16) And everyone understands God to be this [First Unmoved Mover].

Mariusz Grygianiec - Institute of Philosophy, Warsaw University, POLAND.