The internal senses are discernment, instinct, memory and imagination.  (Boyer 1933, 41- 43)

 

Discernment (sensus communis) is the sensitive faculty which perceives and discerns acts of the external senses and knows all sensible things both proper and common in these acts (Summa Theologica, Ia, q. 78. a. 4)

Cardinal Mercier denies discernment is really distinct from external senses.  Rosmini, on the other hand, says discernment is the very substantial of sensivite life.

 

Instinct is internal sense and the proximate principle by which animals perceive unsensed intentions, danger or pleasure.  It is called the "cogitative sense" in man due to the influx of reason.

 

Memory has a double principle, the phantasm of the external sense and the memory of the past apprehended as past.  The memorative sense is had when unsensed intentions or estimated precepts are retained and reporduced.  The Intellective Memory is the faculty of retaining intelligible species after actual consideration so that through these we are able to understand the same things; this intellective memory is not a distinct faculty but is really indentified with the possible intellect.  Avicenna denied the possible intellect, and only affirmed the separate agent intellect.  Aquinas, e contra, argues that if there is sense memory, intellectual memory is stronger, since the intellect is more stable and immoble than corporal material, (Quod recipitur in aliquo, recipitur ad modum recipientis), and receives memories.

 

Imagination retains sensible species through which it is able to reproduce the sensible object, even if absent.  Among the Modern Philosophers, "creative immagination" is the instrument of some superior faculty, sensible or intellectual, that makes objects from selected elements of different sensibles.  (Boyer 1933, 42)  Man can have creative immagination by new phantasms, never existing before (e.g., a gold mountain), or by the intellect or will for a chosen goal, for utility, for a joke, or for art.  (Boyer 1933, 49)

 

If the innovation is intellectual, it is an "intelligible emmanation".  Archimedes had all the facts about the golden crown alleged to be debased by lead as he soaked in the public bath.  His insight was an intelligible emmanation to use displaced water.  His delight was to scream "I have found it" (Eureka!).  (Perkins 2000, 6-7).

 

How does the mind work while innovating?  The philosopher answers by the study of ultimate causes.  "...we unconciously tend to picture thisn operation and try to form a concrete image of what takes place...But there is no psychophysiological mehcanism to be included in the description of the act of knowing...We are here in a different order -- that of the intelligible."  (Gilson 1956, 219)

 

"Thus the solution to the Thomistic problem of knowledge is only possible when the sensible, which is determined in act and the intelligible in potency, can communicate its determination to our intellict, which is intelligible in act but only potentially determined."  (Gilson 1956, 220)

 

Can science help in this process?  "In short the natural tendency of science is not towards unity, but towards an ever more complete disintegration."  (Gilson 1999, 207)  It is the thinker personally who begins to unify and invent.