(This was originally written in response to a friend’s inquiry. I have edited it only slightly from the original response. Take it for what you will.)
I would say that INSTINCT refers to those pre-conscious, natural drives or impulses which are broadly encoded in the species (self-preservation, sex, aggression, etc.) and are manifest without any prior experience or learning.
ORGANIC refers to a way of doing or behaving which is specifically encoded in the individual for the situation. So, in your example, the instinct is self-preservation and the organic response is to raise the arm in a gesture of protection. That specific gesture may not be organic to someone else.
Also, actions-behavior-gestures can be organic without being connected to instinct. That is, they can be a natural expression of the actor’s Body Life without the psychological component of the instinct.
For example: Running
Running is a natural human activity. One can run in a way that is free and uninhibited; in concert with one’s specific human condition (organic), or one can run in a way that is inhibited or inappropriate in some way (inorganic).
This is all without considering the reason for running.
So, we add a reason. Perhaps one is running in order to win a race. This activity becomes a psycho-physical action (at a minimum, it has a specific intention, grounded in human psychology, and a physical means of accomplishing the desired outcome) but winning a race is not instinctual. It’s a cultivated desire.
Perhaps one is in the woods and sees a bear. Or one is in the desert and sees a water hole. Or one is at the park and sees a man stealing a child. Now, the action is driven by an instinct. In each of these cases running is the action, but the way of running will be very different for each, and it would be inorganic to run away from the bear in the same way that would be organic to run toward the water.
Instincts=species-wide, deep-seated drives, impulses, intentions (again, pre-conscious and sometimes irrational) that are either acted upon or not (Maslow argued that Humans are no longer instinctual, since instincts are actually irresistible and we have figured out how to override them)
Organic=a quality of behavior. How an individual responds to impulse or intention. In concert with one’s specific human condition.
What both of these ideas have in common is a root in the subconscious. In other words, they both arise without conscious effort and become complicated by the interference of the intellect/will. The Actor must develop in her/himself the skill to activate these energies and to channel them without force or manipulation. This is where the performance score is crucial.
Too often, this word ORGANIC gets thrown around very generically. It’s a kind of lingo or acting jargon; it sounds good but usually doesn’t mean anything (or at least doesn’t mean what the user thinks it means). Most often, it gets used in a very general way to mean “natural.” But “natural” is not correct. Natural is not always Organic. Any number of extremely inorganic, formalized behavior can be “naturalized”– Ballet, Gurdjieffian Movements, the slow-motion style of early Robert Wilson, Grotowski’s Plastiques– but they remain inorganic.
I suspect the word is most abused as an actor’s excuse to not do what the director asks them to do; a way to avoid the difficult work. “I can’t do that. It just doesn’t feel Organic.”