McLuhan's method is founded upon the doctrine of the Logos (reason and speech) inherited from ancient Greek cosmology and philosophy.
Notably expounded by Heraclitus in the 5th century BC, by Plato and the Stoics in the centuries before Christ, and later by Aristotle and St Thomas Aquinas who use it to explain causality, Logos presents the universe as a divine utterance with an order, or pattern, analogized in the 'reason and speech' of humankind.
Its development over the centuries is sketched out in McLuhan's doctoral thesis of 1943, while in Laws of Media the McLuhans historicize Logos in relation to modern semiotic theory and linguistics.
McLuhan uses the Aristotelian/Thomist notion of Logos to describe the 'formal cause' as that which is 'duly proportioned' to the senses, however he extends this concept of 'reason and speech' to technologies.
That the speech and artifacts of humankind exist as forms proportionate to the Logos McLuhan accepts as a matter of (Catholic) faith.