It has often been said that the separation between the sides of light and dark can be made by motivation. However this in itself is rather hazy. Take for example, Martin Luther King. Think about his motivations. The first thing most people will come up with is that he did it to help his kindred to be treated more fairly and have equal rights. That is a perfectly logical assumption, but there are other possibilities.
Martin Luther King may have been driven to those actions because he was suppressed and he wanted better living standards for himself. Thinking it through, he wouldn't have stood much change campaigning on his own so the best way is to use the masses to work for him in order to improve his living standards. By getting the masses to work for better conditions for themselves they would also be helping him so they are all better off. now of course there is nothing to say this is true, just as there is nothing to say that he did it through his want to help his kindred and helping himself was a useful by-product.
So this leaves definition by motivation greatly lacking. A person could personally subscribe to either explanation, but who is to say that what they tell everyone else is what they were really thinking. It is also possible that they are driven by subconscious motives that they don't even realize they have, that is not to say that all possible subconscious motives are manifested into all individuals. It is hard to prove or disprove the existence of these motives so it really depends on whether or not you are critical or believe it to be a solid conscious decision. A light sider may be driven by will to help themselves without realizing it, and to the same token a darksider may be driven by the will to help others. No matter which motivation you think you are using, the truth is that most people will have both of these types of motivations and many more in them when they choose to take an action. So if it is motivation that makes a person Light Side or Dark Side then it is not the actual motivation, but what they believe to be the motivation that defines what they are. I can't help but feel that this is a superficial way of deciding ones path and hence there must be more to it, yet every reason I examine comes down to the same thing as motivation.
When it comes down to it the apparent difference between the light and dark side is no more than the way you look at things. Each being a different subjective viewpoint on the whole. As a result, these subjective viewpoints can be useful to help us build up a perception which is as accurate as possible of the whole, so they are by no means useless. While the roots may be in the difference between mind-set and interpretation, the manifestation can be seen in differing ways of acting and responding both internally and externally to specific stimuli. Often you will find that people will try to define the different aspects by these resultant actions and responses, but in doing so great gaps are opened up and major overlaps can be found. Whilst observing these actions and responses may be a relatively firm indicator of the root aspect which leads arise to them, it is by no means perfect and if relied on too much can become more of a hindrance than a help.
What leads me to feel that restricting my actions and responses to those characteristic in the root of a specific side is a cramping and a flawed method of approach can be found in the embodiment of the following story about an elephant and four blind men which you may have heard before in one of its various forms.
Four blind men were stood up next to an elephant. Told only that there was an object which they are allowed to touch once in order to identify it.
The first man steps up, feels the tail and proclaims the object to be a brush.
The second steps up, feels the torso and proclaims that it is a hippo. The third steps up, feels the trunk and proclaims it to be a snake. The first three men spent the rest of the day arguing whilst the fourth man walked away smiling knowing that the object was an elephant without even touching it.