He was an opponent of latitudinarianism, associated with Henry Dodwell, George Hickes, Thomas Hearne and John Edwards.
According to Anthony à Wood Proast was first expelled by Finch for "not giving his vote for the warden when he stood to be History Professor and for being meddling and troublesome in the house.
In the anonymous reply, The argument of the Letter concerning toleration, briefly consider’d and answer’d (1690) he advocated for the possible moderate use of force in matters of religion.
[8] Proast's main point was that coercion may not lead directly to changed understanding of religion; but indirectly certain uses of force may actually inculcate beliefs or make the mind receptive to them.
[11] In this later letter, Proast expanded on his arguments, arguing that good ideas have sometimes needed force, while bad ideas have expanded because of force: "Neither does the true Religion always prevail, without the Assistance of the Powers in being; nor is it always the true Religion which does so spread and prevail"[12] Proast also argues against Locke's suggestion that each national religion sees itself as equally valid for civil protection, since French Catholicism was a false religion, French laws requiring subjects to attend mass "can be no Laws, which require men to go to Mass; unless Man can make Laws against God's Laws" [13] After a pause Locke produced a Third Letter later in 1692.