Thank you for subscribing to Annotated Thomist...check back each day for a new section of St. Thomas' corpus, annotated and summarized. (FREE TRIAL FOR NEW SUBSCRIBERS!!!)
AT is also available to donors of $10 or more on Patreon along with all of the other benefits (daily bonus videos, bonus articles, PDFs, etc.
If you need more personalized help reading the Summa, I am available for 1-on-1 sessions, here.
cf., Sent.I.D12.Q1.A3, Graecorum.Part2.C9
Here, he discusses the relationship between the Father and Son in this procession, first, whether there is any distinction in the manner in which the spirative power is possessed, second, whether this makes two principles of the Spirit.
Here, it is important to note a very important distinction between Latin and Greek authors.
Latin authors tend to use "from" for "any derivation from a source of any kind." On the other hand, Greek authors tend (although, not exclusively) to use "from" for simply the derivation from an αιτια, which is unfortunately simply translated as principium by Latin authors.
Αιτια tends in later authors, although not exclusively, to refer to the ultimate underived cause or source of some thing. Whereas principium refers to the cause or source of some thing, abstracting as to whether it is underived or derived. Further, the prepositon "from" in Greek refers to derivation from an αιτια, whereas through denotes derivation from a cause or source that is itself derived.