False Blocks

[nygiants10]

The example states that, "Each rock classic is immediately preceded on the CD by a new composition." I understand why the diagram NR with a block around it is incorrect. However, it says that the correct diagram is R ---->NR with a block around NR, but I thought the answer would be R ---->N. I do not understand why it has to be NR with a block around it.

I would really like it if someone could clear this up. Thank You.

[Nikki Siclunov]

Hey nygiants10,

You are correct in pointing out that we can't simply diagram the rule with an "NR" block (you can have multiple N's in a row). That said, the rule requires that every R be immediately preceded by a N. Thus, if you see an R, then you must have an "NR" block:

R NR

The rule is inherently conditional in nature, because it is only enacted if you have R. Essentially, the rule forbids you from having multiple R's in a row (an inference you can diagram with an "RR" Not-Block). However, it leaves open the possibility that you have multiple "NN" in a row. We can also infer that R cannot be first, and therefore N must be first (assuming a dual-value system).

Finally, the reason why we wouldn't represent this rule as R N is that a rock classic does not simply require a new composition (which is what that rule representation would suggest). Rather, a rock classic requires a new composition to immediately precede the rock classic. Since the necessary condition is inherently linear in nature, it needs to be represented with a block.

Hope this helps!

[nygiants10]

Thank you for your explanation. It really helped.

[T9909]

How come its not written as N.....NR? I'm sure the answer if very simple, but I just don't see it.

[Shannon Parker]

How come its not written as N.....NR? I'm sure the answer if very simple, but I just don't see it.

The arrow indicates a conditional relationship. The block is to illustrate something that must occur. If you have R, it must be proceeded by N. That is why the correct diagram is
N--->NR (with a block).

Hope this helps.
Shannon

[T9909]

Apologies I should have written this question a little more clearer.

Why wouldn't we write the rule out as N--->NR? In the answer above it's written as R--->NR.

Thank you!

[Jonathan Evans]

Hi, T9909,

It's written as R [NR] because R is what triggers the block. Let's review the clue:

• Each rock classic is immediately preceded on the CD by a new
  composition.

What do we know if a new composition (N) is placed in space 3? Do we know that a rock classic (R) is placed in space 4? Not necessarily!

We know that each R must be preceded by an N, but not vice versa. We don't know that there must be an R after every N.

If we have a R, then we know we have [NR] (R [NR]).

If we have an N, then we don't know for sure!

That's why it's not written as N [NR]. This is incorrect. We do not know this for sure.

I hope this helps!

[T9909]

Thank you so much!! Very helpful!