Taken from Turretin in rough outline form:
A thing may be contingent in two ways:
- by depending on God as first cause (as all of creation is thus contingent, since God didn’t have to create)
- by depending on prior second causes (which produce or not produce their effects). Turretin is speaking these contingents.
A future contingent implies both certainty of event and mode of production. As future it is certain, but as contingent in its mode of production. It has the former from the decree of the First Cause, the latter from the constitution of the second cause.
The mode of production is clarified by the Westminster Confession of Faith V.2: It identifies God as the First Cause, corresponding with the first point made by Turretin, but notes that the First Cause orders the events to happen in three modes: freely, necessarily, or contingently.
An event can be both infallibly certain yet contingent. Thus, all things take place by the necessity of consequence, not the necessity of the consequent. Turretin notes that man’s actions can be free because they are spontaneous and follow rational judgment, but necessary because of God’s decree (I: 211).