"That is one thing I do not get with TKD the block are a deflection of the blow but does no real damage". (terryl965)..............
There are more than a few interpertations of TKD, that have different backgrounds. Here is one more that also fits into the equation, Hapkido/Aikijujitsu. Terry's reference to the "deflection" is basis for this assessment. There can be, IMO, a merging of the two aspects of blocking. One can make their block hard and inflict damage or they can just as easy make it a deflection and use it as a base for something else. The one main thing that I have found thru my journey within the arts is that they are all inter-related.
It seems to me there are at least three things you can do with a block:
(i) you can perform it as per a very literal interpretation of the hyung, but harder, so it becomes a damaging strike to the place that it's supposed to come into contact with, going by the most obvious bunkai for the form.
(ii) you can perform it as a strike, but to a very different place, which you have made vulnerable by carrying out the moves concealed within the hyung. An example: your assailant, facing you, grabs the front of your shirt or whatever you're wearing, preparatory to punching your lights out. You grasp his gripping wrist with your right hand, pull it towards you while turning 90 degrees away from him, and bring your left hand up toward your right ear, contacting his gripping arm with your forarm halfway between his elbow and his shoulder---voila, an arm lock!---which you then put pressure on to force him down, lower and lower---and then, with his head moving doward towad yourt hip, you carry out your down `block', which has become hard strike to his lowered throat. Perfored somewhat differently, it's an armbar across his neck, forcing him to the ground... but in any case, you've got a decisive end to the attack right there.
(iii) you can perform it as a throw, e.g., the double block in Palgwe Oh-Jang, which begins with a simultaneous middle outward block (left arm) and rising block (right arm). The way this palgwe plays out, taking these arm moves to be the blocks as described makes little sense... but they make a lot of sense if you take the simultaneous block to be an arm lock where the rising block forces the assailant's arm up at the wrist, the outward block is the corresponding move at the assailant's elbow (where the `block' encodes a grip and an outward forcing move in tandem with the forcing move on the assailant's elbow). This will force the attacker's body down, and the subsequent uppercut in the palgwe should be a decisive finishing strike to the attacker's neck at the base of his skull.
Over and over again, I keep seeing the way `blocks' actually represent highly effective locking and throwing moves... grappling techniques, in fact; and setups for finishing strikes. These are probably the most combat-effective ways of looking at blocks. In their book
The Way of Kata, Kane and Wilder give a number of rules for decoding combat applications of Karate kata---with Goju Ryu karate examples, but their point is that the rules work generally---with their 8th rule being, `There is no block'. I suspect they've derived this rule from Abernethy's rules for kata bunkai in his
Bunkai Jutsu book, in particular his third rule: `All kata applications are designed to end the confrontation instantly', with a number of blocks used to illustrate---and reinterpreted so as to conform to---that rule. Blocks emerge from these guys' interpretations as traps, components of locks, strikes to exposed vital regions, interceptive strikes... but never as purely defensive moves restricted to keeping you from getting hit.
For an orgy of blocks-as-counterattack-components, check out Rick Clark's
75 Down Blocks---a really astonishing book in which he does, really, give 75 different interpretations for the lowly down block, and the ones in which the block is just a block turn out to be essentially hopeless as fighting techniques. In the vast majority of Clark's applications for the down blocks, the block is a lock/throw/strike etc., and the technique is severely effective.