 Science, in the sense of knowledge, falls into one of three kinds: (i) that which is primarily oriented to and necessary for salvation; (ii) that which is useful in the search for truth and righteous living—for living an honest life—but not sufficient for salvation; (iii) that which is useless in both respects and is connected with vanity (DOS 1–2). This grouping obeys a general principle, originated from Augustine, which sets up the direction for medieval learning: knowledge must be directed towards virtue (DOS 639). This same aspect is also present in the consideration of the order of the sciences, in which all sciences are preparatory to the science of the higher end: all sciences are subordinated to, or at the service of (famulantur), theology.