Preface: I first encountered the following on p 83, Philosophy: A Complete Introduction (2012) by Prof Sharon Kaye (MA PhD in Philosophy, U. Toronto). I already tried, but do not see a modern paraphrase by, Early Modern Texts.
Source: Of Liberty and Necessity (1654), § 30, by Thomas Hobbes
§ 30. [...] [1.] So that whereas it is out of controversy that of voluntary actions the will is the necessary cause, and [2.] by this which [3.] is said the will is also caused by other things whereof [4.] it disposes not, it follows that voluntary actions have all of them necessary causes and therefore are necessitated.
How do you parse by this which? Is this one Constituent (Prepositional Phrase) with by as the head? Or are these two Constituents: 1 Prepositional Phrase by this + 1 Relative Pronoun which?
What is the subject of is said? I am inferring that (the entire subordinate clause) 1; but even in 1600s English syntax, did [3.] not need a dummy pronoun 'it', because Subordinate Clauses cannot themselves say anything?
Please advise if my interpretation of 4 is incorrect: 'the will arranges/controls/resolves'.