These three basics are pretty similar looking! I’d suggest thinking of them as a gradation along one axis: how much the foot lifts and articulates.
- First comes the shag basic - shuffle basic, where the ball of the foot stays closer to the floor, making the shuffle.
- The shag basic - arthur murray basic brings the toe to a point behind the body.
- The shag basic - stab basic is where you take the foot back lift and touch the toe down in a “stabbing” motion.
Here’s a little clip of the three, one after another. I didn’t go “full out” in the dancing, my apartment is a bit cramped, but it does show the basic idea of the foot articulation that distinguishes the three.