The medium which bridges the two dimensions of sila, facilitating the translation of outward behavior into inner purity, is volition or cetanā. Volition is a mental factor common to every occasion of experience, a universal concomitant of every act of consciousness. It is the factor which makes experience teleological, i.e., oriented to a goal, since its specific function is to direct its associated factors towards the attainment of a particular end. All action (kamma), the Buddha teaches, is in essence volition, for the act itself is from the ultimate standpoint a manifestation of volition through one of the three doors of action — body, speech or mind: “It is volition, bhikkhus, that I call action. For having willed, one performs an action through body, speech, or mind.”
from http://www.accesstoinsight.org/lib/authors/bodhi/wheel259.html
The Pali word cetanā is variously translated as volition, choice, intention or will. In the Mahayana Buddhist tradition, the Abhidharma-samuccaya states:
What is cetanā? It is a mental activity that propels the mind forward. It has the function of making the mind settle on what is positive, negative, or indeterminate.
Can we identify this force called cetanā within ourselves? It’s partly our thought habits, partly our blind spots, and partly the things we “naturally” move towards and move away from.
The choices that we make are revealed, hour by hour, through our words and actions. For example, if we are extremely averse to confrontation, we may sidle away from difficult encounters. Sometimes the consequences are not serious, but sometimes we end up in places we’d really rather not be. If our cetanā were thoroughly trained towards the wholesome, things would unfold with less friction.
But our intentions are often mixed. We incline toward the wholesome, except in circumstances where we don’t; we love our comfort and this sometimes clouds our vision. We can train our minds to recognize what inclinations are moving behind our actions and words. This is a fruitful form of mindfulness; this is how we re-train ourselves toward freedom.