Practical Application of the Double-Knife-Hand Block

[Danny T]

I've seen that video before and I completely disagree with many of his points, to include:

• "There is no such thing as a chambering motion" - I find this to be absolute rubbish, as my understanding is EVERY technique has a chamber. He also shows several chambering motions in the rest of the video
• At 0:45 he shows a strike which has very little power as it's twisting across your body
• At 1:15 he shows the motion of the off-hand as going from the rear forwards, and then his application of that motion goes from the front backwards (which means the application is of a different motion)
• At 2:15 he makes the claim that no technique ends in a block, which is just absurd to me. It's possible you may need to block multiple attacks in a row. It's possible after blocking an attack your opponent moves out of range. It might be something that is a bit of a school mantra (i.e. always strike after a block) or something like that, but it comes across as a universal claim that doesn't ring true to me.
• At 2:30 he shows that the punch will go right through the block, which means he's doing the block wrong. He also does straight-on blocks later in the video.
• At 2:55 he does the exact opposite motion, but ends in the same spot, and calls it an application of the motion. Which is like using an inward hook punch to explain the motion of an outward block. The technique he's trying to explain has a clockwise motion, he moves counter-clockwise and ends in a similar position, and thus calls it an application of the technique.

This guy contradicts himself plenty of times in the video, makes tons of generalizations that aren't true or aren't well explained in the video, and he will show Movement 1, and then in explaining why you practice that movement, he'll do something completely different.

You disagree...Okay with me.
I don't agree with everything he shows or states in the whole video.
I first stated it is a movement. What is important is what can be performed within the movements. Then made reference to some potentials. The video is an example of some of the potentials I referenced as well as some others.
Have a nice day.

 

[skribs]

Unless I'm misunderstanding you, you are asking about keeping a hand pressed to your solar plexus as opposed to letting it float an inch or two away.

That is just aesthetics. There's no functional difference between the two. The principle being demonstrated is the same. Details are important but not every detail. Over focusing on minutiae diminishes you.

As the other poster's pointed out techniques are just a top layer to understanding forms.

Well that's the layer I'm working on right now.

Ok, lets be fair... he never said what you quoted in the video shown. (I watched it 3 times, listening for that phrase... if I missed it, please give the time when he says it) What he did say was that the chambering motion was the block. So of course he will continue to show the chambering motion, thats the blocking part of the technique, for the purpose of his discussion.

Hmmm...you're right. I'm sure I heard it the first time I watched it, although that may have been another video I found on the subject around that time. Still, the way he states it adamantly that the chamber is a block, then later on he uses that motion as a chamber for a knife-hand block. It would have been more accurate if he said "it can be a palm block followed by a knife-hand strike" instead of definitively stating that the chamber is not a chamber.

Well, what are you expecting us to do for you?

Apparently, you were taught:

• A chamber is only a chamber, and is only used to load a strike. - It cannot be anything else.
• A knife hand block is a block, to a specific target on the forearm, with a specific shape of your hand, impacting with 2 inch blade of your hand. - Therefore it can be nothing else, if it hits a bicep or neck, you are doing it wrong.
• Your other hand in this art is a second knife hand block. - Therefore, it must be a block, where your 2 inch blade on your hand, is impacting that same specific target on the forearm of the attacker.

So, at this point, I am not sure how to answer your question.

• Where did I say a chamber is only a chamber? I'm specifically discussing his position that the chamber IS a block and the block IS a strike. He was the one stating it definitively.
• Actually a knife-hand block should use the blade of your hand or the forearm. That's the reason the motion is the way it is (a push outward with your forearm). If it's used as a strike, it's less effective than if you were to do a knife-hand strike motion. It's just like if I do a front pushing kick instead of a front snap kick. The push serves a purpose of getting the opponent away from you, but it's not as effective as a strike at penetrating into soft tissue or snapping back joints. A pushing kick to the head isn't likely to knock an opponent out, but send him off-balance. Similar motions, but different. Different techniques and different applications. By the way - this isn't specifically what I was taught. This is what I've seen. People who have the same motion for a knife-hand block and a knife-hand strike typically have weaker knife-hand strikes. Those who have the motions specific to the block and strike tend to have sharper versions of both techniques.
• Um...I have never said that, nor have I said anything remotely like that. Your other hand is held at your solar plexus in the double-knife-hand technique as I described. I am not saying that hand is blocking. I am saying that, if the double-knife-hand block is being used as a block (as the name applies) what is the other hand doing? That is my question.

I am specifically trying to understand the motion as it pertains to a block.

The answer is: it is a block, with your knife hand, that covers the solar plexus. It must be that, since you disagree with any interpretation that does not involve a knife hand block, blocking with the knife edge of the hand, to the attackers forearm. Since that is the only answer you will accept, why ask the question, when you know the answer?

Alright, I admit, I am just some lazy keyboard martial artist, meta pontificating about stuff that I apparently know nothing about, so that I will look good... And while you have a way better understanding of martial arts than I do... there are people on this site, this thread even, who have forgotten more about martial arts than you and I combined will ever learn to begin with. I try to take their advice and suggestions. But, thats me.

In the scenario that:

• You are doing a double-knife-hand block with the left hand blocking and the right hand at your solar plexus
• And you are using this motion to block a punch

What is the reason why your right hand is at your solar plexus?

That is the question. It is a block...with the left hand. So what is the right hand doing?

I'm not denying that a lot of people on this forum know a lot about martial arts. What I do wonder is:

• Do you understand the question that is being asked? Because everyone's focused on meta knowledge and details that have nothing to do with the question of single knife-hand block vs. double-knife-hand block.
• Do you know the answer to the specific question I am asking? If you know millions of answers, but not the one I am asking, then those millions of other answers are not helpful in helping me answer this question.

As to meta-knowledge...if I am trying to block a punch, does it matter if I know that I can also use a knife-hand for a strike or a similar motion for a grappling move? Or does it matter that I know how to block a punch?

You disagree...Okay with me.
I don't agree with everything he shows or states in the whole video.
I first stated it is a movement. What is important is what can be performed within the movements. Then made reference to some potentials. The video is an example of some of the potentials I referenced as well as some others.
Have a nice day.

The video is an example if you take a motion with an end position, ignore the motion itself but find several other ways to get to that end position, and call it good. If I do a roundhouse kick or a hook kick, my foot will recoil back to roughly the same position before I reset my stance. So if someone asked how a hook kick is practical, could I show them a roundhouse kick and say "see, look, my leg's basically in the same spot at this point in time, so that's the application of a hook kick."

It's absolutely ridiculous when you think of it like that. That's why I consider it ridiculous to take a motion flowing outside, and take another motion flowing inside, and call the second motion an application of the first.

 

[skribs]

To be clear, what I am trying to do is analyze this specific technique, in this specific application, as to why you position your off-hand the way it is positioned.

All other applications, all other similar motions, are irrelevant to the question of why your other hand is held at your solar plexus in a knife-hand block instead of in a guard position in front of you (i.e. next to your other hand's elbow) or tight at your side (like the single knife-hand block).

Everything else is irrelevant to why I asked this question. I am not saying it can only be a block. I am saying, for the purpose of this question, I am only focusing on the technique as it is named - the block. This is my problem with all of the meta-discussion. It's extra information that is irrelevant to what I am specifically seeking to learn. I am not saying that this cannot be used for grappling. I am saying I specifically want to look at it as a block, for now, for this very question, so I can understand it's application as a block, as it is described in the forms and manuals.

I am not saying it can't be used for grappling. I am saying, it is named as a block, it is described as a block, so how does it work as a block?

And in particular, the double knife-hand as opposed to the single knife-hand, what is the reason for that position in a block?

 

[wab25]

In the scenario that:

• You are doing a double-knife-hand block with the left hand blocking and the right hand at your solar plexus
• And you are using this motion to block a punch

What is the reason why your right hand is at your solar plexus?

That is the question. It is a block...with the left hand. So what is the right hand doing?

In this specific scenario, what is the right hand doing? Nothing.

You could put it into guard, put it into chamber, put it in your pocket or drape it by your side. Its doing nothing.

So, why is it there? Well... it has to go somewhere. As long as it has to go somewhere, it may as well go someplace that will eventually be useful. When we get to other scenarios and other situations... it being there will have a purpose and a reason. But, for this situation, where we are blocking a punch with the left forearm and knife edge... the right hand is doing nothing.

 

[skribs]

In this specific scenario, what is the right hand doing? Nothing.

You could put it into guard, put it into chamber, put it in your pocket or drape it by your side. Its doing nothing.

So, why is it there? Well... it has to go somewhere. As long as it has to go somewhere, it may as well go someplace that will eventually be useful. When we get to other scenarios and other situations... it being there will have a purpose and a reason. But, for this situation, where we are blocking a punch with the left forearm and knife edge... the right hand is doing nothing.

Thanks for your reply.

Since you have to put your hand somewhere, why doesn't it go tight at your side (as with most other techniques), into a guard, or into a chamber? What is the advantage of it being here, instead of one of those three other locations (guard, tight, chamber). In a pros-and-cons sort of way, what are the pros of doing this instead of the others?

If it is to set up something else, after blocking a strike with your blocking hand, what techniques would follow in which it is beneficial to have your hand at your solarplexus instead of in a guard or tight at your side?

 

[wab25]

Since you have to put your hand somewhere, why doesn't it go tight at your side (as with most other techniques), into a guard, or into a chamber?

Since we are talking about this situation, where the left is blocking a punch as the name indicates... there is no reason why it goes there. It will only mean anything at all, in that position, once we can consider other applications of this movement. Until then, there can be no reason for it to be anywhere, as the other hand is doing the block.

What is the advantage of it being here, instead of one of those three other locations (guard, tight, chamber).

In this situation, there is no advantage, no pros and no cons.

If it is to set up something else, after blocking a strike with your blocking hand, what techniques would follow in which it is beneficial to have your hand at your solarplexus instead of in a guard or tight at your side?

Its not beneficial. Thats why, when you are sparring, and you use a knife hand block, you do not put your other hand here. Hopefully, you keep it in guard and / or counter with the other one.

The only reason for this part of the movement, is for other applications of the movement, besides knife hand blocking with the left.

 

[skribs]

Since we are talking about this situation, where the left is blocking a punch as the name indicates... there is no reason why it goes there. It will only mean anything at all, in that position, once we can consider other applications of this movement. Until then, there can be no reason for it to be anywhere, as the other hand is doing the block.

In this situation, there is no advantage, no pros and no cons.

Its not beneficial. Thats why, when you are sparring, and you use a knife hand block, you do not put your other hand here. Hopefully, you keep it in guard and / or counter with the other one.

The only reason for this part of the movement, is for other applications of the movement, besides knife hand blocking with the left.

This is the problem I have, and the reason for the question. It exists in both the Karate and Taekwondo katas/poomsae. Both call it a block, so the block must be at least one application for the technique. But I'm struggling to find why this is a preferred position for your off-hand in a blocking application.

 

[Jaeimseu]

In Taegeuk 4, the double knifehand blocks are followed by a spearhand, a sidekick, and a turn in another direction. In these cases, it could be argued that the hand positioned in front of the solar plexus minimizes excess movement in the transition to the following technique.

In Taegeuk 6, double knifehand block is followed by double knifehand block and a palm block. The same argument could be made here.

In Taegeuk 7, double knifehand block (low) is followed by double knifehand block and then a supported palm block. I think it’s the same here.

In Taegeuk 8, it’s followed by a front kick. The difference here is that while it’s done from back stance previously, it’s done here from tiger/cat stance. It makes since that the offhand is at the solar plexus since cat stance is more forward facing than back stance.

Single knifehand blocks occur in Taegeuk 3 (followed by a change to front stance and reverse punch), Taegeuk 5 (followed by a step forward into front stance and elbow strike), and Taegeuk 8 (followed by a change to front stance and an elbow strike). I’d say that in these instances the follow-up technique is better suited having the hand further back (at the hip in these cases).

Of course, there are other occurrences where the follow-up is the same regardless of the initial block being single or double. In Taegeuk 8, the follow-up of the first double block (closed fist in this case) is a switch to front stance and a reverse punch, just like the single knifehand block in Taegeuk 3.

Anyway, that’s one possible explanation. Maybe someone else can analyze follow-up techniques in the Chang Hon Hyeongs or Palgwe poomsae.


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[Kung Fu Wang]

What is the purpose of doing a double-knife-hand block instead of a single knife-hand block?

You use one hand to control your opponent's elbow joint while use another hand to control your opponent's wrist joint.

 

[Gnarlie]

Investigate the meaning of 막기 skribs. It does not only mean block.

That said, it is there in this technique as a block IMO to show you early on in your learning that two handed techniques exist. Later in your learning you will see why it makes sense to have the hand ready at the solar plexus when performing a motion with the front hand, for a number of reasons.

If double hand motions were not included in the early forms, you'd never know that it is OK not to pull back to the hip.

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[Gnarlie]

You use one hand to control your opponent's elbow joint while use another hand to control your opponent's wrist joint.

Or one hand for the head and one for the elbow. Or one for the foot and one for the knee. And so on.

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[wab25]

This is the problem I have, and the reason for the question. It exists in both the Karate and Taekwondo katas/poomsae. Both call it a block, so the block must be at least one application for the technique. But I'm struggling to find why this is a preferred position for your off-hand in a blocking application.

The reason for the preferred position for your off-hand in this movement, is for the other applications. The reason this movement is called a block is as a teaching aid for beginners. By looking at it as a block, beginners can learn the mechanics of it, the speed, power and control. Once the mechanics are learned, the application of those mechanics opens up to a wide variety of things. Other arts, put the off hand in other places. The knife hand blocking application, is just as effective. But, the other applications that that art looks at the most, will determine where the off hand goes.

Calling movements "punch," "block," "kick," "throw," "joint lock," "chamber..." is a great teaching aid. What is being taught is body mechanics. These aids help teach the body mechanics fairly quickly. These aids can become blinders though, when we limit the movement to the name. Once we limit the movement to just the name, many parts of the movement are no longer necessary or effective. However, removing the unnecessary and ineffective pieces, limits the deeper application of the movement. Once you learn the movement, throw the name away and play with the movement.

 

[skribs]

You use one hand to control your opponent's elbow joint while use another hand to control your opponent's wrist joint.

If it's going as I imagine, then we are thinking of two completely different techniques.

Investigate the meaning of 막기 skribs. It does not only mean block.

That said, it is there in this technique as a block IMO to show you early on in your learning that two handed techniques exist. Later in your learning you will see why it makes sense to have the hand ready at the solar plexus when performing a motion with the front hand, for a number of reasons.

If double hand motions were not included in the early forms, you'd never know that it is OK not to pull back to the hip.

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There are other two-handed techniques we have that make more sense, such as a block with one hand and strike with another, or two-handed blocks that make use of both hands in the blocking motion (i.e. a cross block). Why not use one of these techniques instead?

The reason for the preferred position for your off-hand in this movement, is for the other applications. The reason this movement is called a block is as a teaching aid for beginners. By looking at it as a block, beginners can learn the mechanics of it, the speed, power and control. Once the mechanics are learned, the application of those mechanics opens up to a wide variety of things. Other arts, put the off hand in other places. The knife hand blocking application, is just as effective. But, the other applications that that art looks at the most, will determine where the off hand goes.

Calling movements "punch," "block," "kick," "throw," "joint lock," "chamber..." is a great teaching aid. What is being taught is body mechanics. These aids help teach the body mechanics fairly quickly. These aids can become blinders though, when we limit the movement to the name. Once we limit the movement to just the name, many parts of the movement are no longer necessary or effective. However, removing the unnecessary and ineffective pieces, limits the deeper application of the movement. Once you learn the movement, throw the name away and play with the movement.

If that's the case, why not teach the application that uses the entire motion as the application for the technique?

I can somewhat see that in the way we teach certain techniques, we only teach part of the technique at first. For example, when we teach kids punches, we teach them to keep their feet still (so they're not running around while they punch), and the first ax kick we teach is straight up and down (instead of later when we do more practical versions of the ax kick). However, the double-knife-hand block we teach pretty much the same from when it is learned, so it's still a bit of a different principle. Especially since the motion continues to show up in black belt forms like Koryo and Taebaek.

 

[Gnarlie]

If it's going as I imagine, then we are thinking of two completely different techniques.



There are other two-handed techniques we have that make more sense, such as a block with one hand and strike with another, or two-handed blocks that make use of both hands in the blocking motion (i.e. a cross block). Why not use one of these techniques instead?



If that's the case, why not teach the application that uses the entire motion as the application for the technique?

I can somewhat see that in the way we teach certain techniques, we only teach part of the technique at first. For example, when we teach kids punches, we teach them to keep their feet still (so they're not running around while they punch), and the first ax kick we teach is straight up and down (instead of later when we do more practical versions of the ax kick). However, the double-knife-hand block we teach pretty much the same from when it is learned, so it's still a bit of a different principle. Especially since the motion continues to show up in black belt forms like Koryo and Taebaek.

Because those techniques don't afford the same result in the same circumstances.

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[WaterGal]

I am specifically referring to the double-knife-hand block that typically shows up in Taekwondo forms, such as Palgwe Il Jang or Taegeuk Sa Jang. Where the blocking hand is a knife-hand block with the palm out, and the other hand is held around your solar plexus, palm up..

If we're looking specifically at Taegeuk Sah-jang (I don't know Palgwe forms, so I can't speak to them), the hand at the solar plexus is about to be used for a spearhand technique. The hand needs to be open and lined up with the target before you do that strike, right? So the double-knifehand block does that.

When we see it again in Yuk-jang, the hand that's open at the solar plexus then does a palm block at the chest level.Then in Chil-jang (low block version), the open hand at the solar plexus turns into a grab across the body. I suppose you could do these techniques while starting with a closed fist at the hip, but having the hand open and at the solar plexus cuts down on the time needed to the do the technique.

 

[skribs]

If we're looking specifically at Taegeuk Sah-jang (I don't know Palgwe forms, so I can't speak to them), the hand at the solar plexus is about to be used for a spearhand technique. The hand needs to be open and lined up with the target before you do that strike, right? So the double-knifehand block does that.

When we see it again in Yuk-jang, the hand that's open at the solar plexus then does a palm block at the chest level.Then in Chil-jang (low block version), the open hand at the solar plexus turns into a grab across the body. I suppose you could do these techniques while starting with a closed fist at the hip, but having the hand open and at the solar plexus cuts down on the time needed to the do the technique.

Oh ok. We mainly do the Palgwe forms at my school (and different versions from most of the Palgwe forms I've seen online).

In our Palgwe #1, after the double-knife-hand, the next technique is an inside block, so you move from your solar plexus to your ear to chamber the inside block.
In Palgwe #2, we do low double-knife-hand, then mid, and then a single high block, and I guess I can see how the flow is better there.
In Palgwe #3, same thing with transitions from double-knife hand to double-knife hand.
In Palgwe #4, we do something similar to Taegeuk #4, except with an added step. Double-knife-hand (left hand blocking), then a palm block with the left hand, and then a spearhand with the right. With the palm block, the right hand comes tight at your waist. It does give the palm block a bit of that torsion (similar to any technique where the other hand comes to your waist).
In Palgwe #6, there is a grab after the double-knife-hand block, which I could see being faster from the solarplexus.

So I guess it doesn't make sense to me in all of the forms over other options available, but it is starting to make sense to me if I look at specific forms. I think the problem is I was always looking at the forms in which it makes less sense to me and trying to apply it. Where if I look at how it's used in Form 2 it makes a lot of sense.

Thanks!

 

[wab25]

If that's the case, why not teach the application that uses the entire motion as the application for the technique?

Which application? You would still have to choose. However, I believe the different arts already chose.

What is the important part of the technique? It's not the block. The important part of the technique, is the body mechanics. (for this discussion, body mechanics includes balance, power generation, speed, control...) All applications of this technique, must contain all the important parts of the technique... that is the body mechanics. The different applications may change the unimportant parts (where the arms and hands go, and what shape they hold), all they want, so long as the body mechanics remain the same.

In TKD and Karate, this technique is taught as a block. In Aikido, this technique is taught as an off balancing or structure break (many times followed up with an armbar). In Judo, this technique would be taught as a throw. In jujitsu, as a choke. I have done this technique (same body mechanics) in these arts, for these different applications (most of the time with the hands in the same places). This is one of the things that I appreciate about the Traditional MA, many times they have found ways to practice many applications, in a single set movements.

Many have posted with TKD specific things that follow in forms, as reasons for holding the hand there. Thats what the forms / kata hold... not just a list of individual techniques, but also the transitions and flows between them. The different arts do different forms / katas with different combos, because their founders were different people who found things in different ways and organized things differently when trying to teach. WaterGal mentioned this would be followed with a spearhand, as in block, then strike. Nothing wrong with that at all. Another way, would be to do the same knife hand block and spearhand after the other guy grabbed your left wrist with his left hand. This would break his structure, off balance him and the spearhand would effect an armbar. They are both great, both effective. But, there are a ton of additional applications, and other places to flow to. This would explain why this technique keeps showing up again and again in different forms... to show different movement flows, for different applications. Consider not only what follows, but also what precedes.

 

[skribs]

Which application? You would still have to choose. However, I believe the different arts already chose.

What is the important part of the technique? It's not the block. The important part of the technique, is the body mechanics. (for this discussion, body mechanics includes balance, power generation, speed, control...) All applications of this technique, must contain all the important parts of the technique... that is the body mechanics. The different applications may change the unimportant parts (where the arms and hands go, and what shape they hold), all they want, so long as the body mechanics remain the same.

In TKD and Karate, this technique is taught as a block. In Aikido, this technique is taught as an off balancing or structure break (many times followed up with an armbar). In Judo, this technique would be taught as a throw. In jujitsu, as a choke. I have done this technique (same body mechanics) in these arts, for these different applications (most of the time with the hands in the same places). This is one of the things that I appreciate about the Traditional MA, many times they have found ways to practice many applications, in a single set movements.

Many have posted with TKD specific things that follow in forms, as reasons for holding the hand there. Thats what the forms / kata hold... not just a list of individual techniques, but also the transitions and flows between them. The different arts do different forms / katas with different combos, because their founders were different people who found things in different ways and organized things differently when trying to teach. WaterGal mentioned this would be followed with a spearhand, as in block, then strike. Nothing wrong with that at all. Another way, would be to do the same knife hand block and spearhand after the other guy grabbed your left wrist with his left hand. This would break his structure, off balance him and the spearhand would effect an armbar. They are both great, both effective. But, there are a ton of additional applications, and other places to flow to. This would explain why this technique keeps showing up again and again in different forms... to show different movement flows, for different applications. Consider not only what follows, but also what precedes.

Like you said - pick one. Pick whichever one makes full use of the motion and makes the most sense based on either it's position in the kata or on it's frequency in your curriculum.

To use another motion, let's take a knife-hand block to block a punch, a palm strike to counter, and then turning around while pressing up and back on the chin, and pulling down and twisting the wrist to effect a take-down. I could do a similar motion after doing a knife-hand block and palm strike, to turn around and do a downward palm block. It would make some sense in the form, so you could do that. But if the actual application of the motion is to enact a throw, then that could be taught instead.

This is why I wanted to isolate one aspect of the technique, and in particular, the aspect of the technique it is named after. The motion I train is "block" in my brain, and I want to reconcile the motion and the application together, which I was having trouble with. I have similar issues with other blocking techniques (such as augmented blocks, or with some of the double blocks you see in Keumgang). I see plenty of applications for some of those techniques if you assume they are not blocks. For example, an augmented block as a grappling break and armbar, or a scissor block as a down block and backfist, or outside block and hammer fist. I see the potential other applications of the movement or similar motions, but I don't see how the technique as named is practical. (And those can be left for another thread).

This is the reason I have been so adamant on coming down to this specific application. In a lot of cases, I understand other applications for a similar motion. But I want to understand this particular application better.

 

[jks9199]

Can everyone please forget about the blocking hand? I'm specifically trying to ask about the OTHER hand. As to why it goes to your solarplexus instead of a typical guard position (i.e. in front of you instead of next to you) or a typical chamber position) i.e. held at your hip or at your neck to prepare for the next technique).

How does it get there? What does it do while it is traveling to that position? I don't do TKD; I don't know this particular form or technique... but that's where I'd start in analyzing an unusual movement during any form or technique. Answer those questions, and we just might discover why it is going there. And, if we don't -- the next question is what does it do afterwards? How does it move from that solar plexus position to whatever it does next?

 

[Danny T]

To be clear, what I am trying to do is analyze this specific technique, in this specific application, as to why you position your off-hand the way it is positioned.

All other applications, all other similar motions, are irrelevant to the question of why your other hand is held at your solar plexus in a knife-hand block instead of in a guard position in front of you (i.e. next to your other hand's elbow) or tight at your side (like the single knife-hand block).

Everything else is irrelevant to why I asked this question. I am not saying it can only be a block. I am saying, for the purpose of this question, I am only focusing on the technique as it is named - the block. This is my problem with all of the meta-discussion. It's extra information that is irrelevant to what I am specifically seeking to learn. I am not saying that this cannot be used for grappling. I am saying I specifically want to look at it as a block, for now, for this very question, so I can understand it's application as a block, as it is described in the forms and manuals.

I am not saying it can't be used for grappling. I am saying, it is named as a block, it is described as a block, so how does it work as a block?

And in particular, the double knife-hand as opposed to the single knife-hand, what is the reason for that position in a block?

You need to do some research into the actual terminology then.
It is actually call uke and the total of the uke techniques are known as uke waza. Uke actually is a receiving action but it's closest translation to English is to stop hence Block.

Uke waza certainly can be used to block punches, kicks and strikes but they are, in fact, much more versatile techniques. To receive denotes one clear a limb, to off-balance, to set up for a strike or throw, or to lock a joint once a limb has been seized. In short, uke waza are not just for blocking and the uke waze movements are to be used in a multitude of applications.

Also movement and position in Kata is working to a precise position where in down and dirty action of fighting getting to a particular position precisely as in Kata may never happen.