Is there a difference between a self defense art versus a combative art?
If so what are the differences?
Sitting home sick with the super flu so I'll take a stab at this.
I do believe there can be differences between the two. A combative art could be something that is like what the military teaches in their programs. I think the Marine Corps have developed a Combative Military Art program for their soldiers that is focused on tactics used for dealing with enemy soldiers.
The importance here is it in the stated objective goals of the instruction, the method of instruction chosen, the techniques that are chosen to support the overall objectives of the system, then the instructors are trained to support the overall goals and they begin teaching the troops. The troops are then trained in a limited number of techniques that can be learned in a short time and drilled and drilled and they do this in different enviroments with different types of gear etc. etc. and everything is rolled up to (including rifle and hand gun training) into them being able to defend themselves and their fellow soldiers. But on top of just defending themselves these skills are also possibly used in meeting the military's objective of taking that country, protecting our country, securing that hill, taking that street or clearing that house. But the hand to hand training, weapon to hand training etc. etc. is designed to support the military's objectives. Any military system is like this to some degree.
Then you have military based programs that were altered for civilians. Say Krav Maga, these are systems that take out the stuff that wouldn't be right for civilians (say sentry killing techniques) and teach more self defense type training. But again the objective has changed more to personal self defense instead of hold that site at all costs (hit them and run away instead of stay here and fight at all costs even death).
Pure self defense related systems don't care about, sparing, dueling, historical techniques, historical styles, masters, grandmasters, ranks, etc. etc. or anyone else but self preservation first and foremost. They don't care about getting in top physical shape (per say) but rather getting their objective met which is not getting assaulted, attacked, threatened, etc. etc. in the first place. So in a sense self defense/protection takes on a different mentality involving not only the mental and physical aspects (in regards to the purely physical reponses of defense against assaults) but also the minimazation of threat exposure before the assualt as well.
Some might say the differences are in the intention. Self defense focuses on escape while a combative art focuses on fighting.
Can they be used both for self defense and combat? Can a self defense art be a combative art? Can a combative art be an effective self defense art or will it become a liability because of the legal system?
I think the differences are instead of intention (if you mean the amount of force or how it is applied) it is rather the objective. In the one it is the person's survival, in the other it is the unit's, military's, goal being met with the person's secondary.
But can the techniques contained within both systems be used, are the techniques similar or the same? For the vast majority (95%+) I would think yes. A very small percentage of the military or the Combative systems, probably not.