What's the difference between a hard & soft, and linear and circular technique?

A linear technique is a straight line technique or method of attack. Front kicks, side kicks, reverse punches, straight right hands are all examples of a linear technique or method of attack. An example of a circular technique or method of attack is a round house, a hook kick or wheel kick, or a hook in punching and they travel other than a straight line and so they generally take a little longer to get to their intended target. They also tend to travel around your opponent's first line of defense which is his arms and hands and his knees and legs. A hard technique as opposed to a soft technique is a little harder for some to understand sometimes. Many but not all soft techniques are open handed techniques and because they are they can usually be done a little more quickly but they also carry the risk of injury to your hands and fingers if not applied correctly. All your hard techniques are close handed and they don't exposed your hands and fingers to the same risk and tend to be stronger but a fraction slower in execution. You see both hard and soft techniques in blocking and punching and striking. Brushing blocks for instance are openhanded blocks where you meet the technique from the side and brush it to the side with your fingers open but together making contact mainly with the open palm of your hand and this works quite well for punches and strikes and some but not all kicks. You also have soft strikes like knife hand strikes, palm heel strikes, and various open handed finger strikes. However I would not recommend you try to block a round house kick with a brushing block or a leg kick. They being too strong and their path of travel being circular it is then pretty easy if you put that hand up or out there to brush them for that open hand and/or fingers to be broken. Instead you would use a close handed block for those techniques. You also have hard techniques for punching and striking and all your punches are that and many would also classify a back-fist as a hard technique also. The other thing about this is what is your intended target. If you wanted to attack nerve centers then open handed techniques would be more effective for that because they allow you to concentrate the impact on a smaller point and more deeply. However the damage they do is very localized to that point where they make contact at. Hard techniques being stronger but hitting with the fist disperse that damage out that they do because of making contact with the fist and are generally stronger.

In the hard styles you use the tension of the body to remain solid when you strike. In the soft styles, your alignment connects your strikes to the ground so you use the ground for solidity and the body can remain relaxed. Also the force comes mainly from the sequential expansion of the joints, from the ground up, through the body. The movement of an arm or leg is just to deliver the wave of force. In the hard styles, it is the movement of the body alone (mass times speed) that creates the force. Hard styles use blocking to push the force of the opponent out of the way. In the soft styles you have to allow the opponent to strike where he wants to, but YOU move out of the way. This requires that you can sense where the striker is aiming before the strike comes out. You therefore have to be able to sense his intention before it manifests into a strike. This requires specialized training. In linear technique the movements come out in a straight line from the origin of the force (hips or legs depending on style) directly to the target. In circular technique, each joint of the body is free to move in an aligned way towards the target. Since the angle of each joint to the target is different from a joint in another area of the body, this results in circularity in the overall movement. Just as the circular movements of a sling (weapon) contribute to a linear effect of the pebble thrown at the opponent, all the circular movements, created by the independent movements of the joints, join up to create a linear movement to the target. However, in this case, if the strike is blocked, the arm, for example, can easily circle around to continue the strike. This is because it is not the arm itself that is creating the force but the movements of each joint of the body. The arm itself is loose until the moment of impact. Circular strikes are very useful when striking with the palm or edge of the fist, especially when hitting the head. In most cases, there is a mixture of hard and soft, circular and linear. My style, Tai-chi-Chuan, is known for being a "soft style" but the strikes are all full force emanating from every part of the body in an explosive way. Soft doesn't mean light force. It means that you don't use any more tension than you have to or any more movement than you have to.

hard: you atttack everything soft: you attack the weak spot