In ocular vision we distinguish three things: the eye, or visual faculty the coloured object, and the light which serves as the medium between the eye and the object.
It is usual to term colour the formal object ( objectum formale quod ) of vision, since it is that which precisely and alone makes a thing the object of vision, the individual object seen may be termed the material object, e.g. Similarly, the light which serves as the medium between the eye and the object is termed the formal reason ( objectum formale quo ) of our actual vision.
If the authority upon which we base our assent is human and therefore fallible, we have human and fallible faith; if the authority is Divine, we have Divine and infallible faith.
If to this be added the medium by which the Divine authority for certain statements is put before us, viz.
(e) We shall arrive at a better understanding of the habit or virtue of faith if we have previously analysed an act of faith; and this analysis will be facilitated by examining an act of ocular vision and an act of reasoned knowledge.
In the same way, when we analyze an act of intellectual assent to any given truth, we must distinguish the intellectual faculty which elicits the act the intelligible object towards which the intellect is directed, and the evidence whether intrinsic to that object or extrinsic to it, which moves us to assent to it.