Hi Snark! I completely agree that the principles of structure are the most definitive. They kinda form the base of the pyramid, without which nothing else can function. Now I should clarify that I am abusing the word 'structure' to include all the movements of the body and limbs, or at least instantaneous snapshots thereof. And yet when I roll with practitioners from other lineages, the differences that I usually feel between us are those of tension and timing. However...(caveat)...differences in tension, for example, are often necessitated by differences in structure. For example, the positioning of his elbow in bong sao may require him to flex his shoulder unduly to ward off a sudden attack. I do like your point about how you can sometimes pick up on some subtle clues that the dude practicing the form might not have intended to display. An example of this might be little vibrations caused by flexion of muscles. So yeah, you can tell a great deal about a chunner's principles by watching his forms but I would still want to touch hands with him before I draw any conclusions about the efficacy of his style. Helps to reduce my diet of humble pie.