Adjective rules

Question

First and foremost, I am a beginner, and I have just started studying Japanese. At my university we use Shokyu Nihongo 1 as the main student, so let's get to the point. In chapter 2 there are rules about adjectives. Thus far I understand the order of adjectives:

1. Noun は Adjective (い-adj or な-adj) です
2. Adjective (い-adj or な-adj) Noun は です

富士山は高い山です。

However I don't understand the difference between rule #2 and #3

The rule #3 is as follows: Adjective (い-adj or な-adj) Noun は ~ です

e.g. そのあかいかみはしょっけんですか。いいえ、このあかいかみはしょっけんではありません。

In my book rules #2 and #3 are the same, however, I may not see the difference so I would be glad for the explanation of rule #3

Answer 1

There are several things potentially going on here there are confusing you.

The first that comes to mind is a grammatical point being somewhat obscured by the use of formal structures.

To me, it looks like there are three different types of sentences you're learning to express here.

1. Noun Phrase is Adjective
2. It is Noun Phrase.
3. Noun Phrase is Noun Phrase

These would correspond to the following three rules for Japanese

1. Noun は Adjective (い-adj or な-adj) です
2. Adjective (い-adj or な-adj) Noun です (Notice this differs from your rule 2)
3. Adjective (い-adj or な-adj) Noun は [Noun Phrase] です

These are expressing three rather different ideas.

Examples first in English.

1. The red book is expensive.
2. It is a tall mountain.
3. The young woman is a student.

In Japanese, using plain forms (which you may not have learned yet), these would be expressed as

1. [赤]{あか}い[本]{ほん}は[高]{たか}い
2. [高]{たか}い[山]{やま}だ
3. [若]{わか}い[女]{おんな}は[学生]{がくせい}だ

To move these into a more formal register, you would change them as follows.

• For sentences ending in an い-adjective, the sentence is made formal by adding です
• For sentences ending in だ, change だ to です

So, applying these to the three sentences above (to make them formal), you get

1. [赤]{あか}い[本]{ほん}は[高]{たか}いです
2. [高]{たか}い[山]{やま}です
3. [若]{わか}い[女]{おんな}は[学生]{がくせい}です

There is no Japanese grammatical structure that is composed as

• <Noun phrase>はです。

If you're starting with <Noun phrase>は and ending with です then between the two you need to be saying something about <Noun phrase>.

So, it's ungrammatical to say

あかいほんはです

The read book is .... <what? you haven't said>

But you can say

あかいほんです

It's a red book.

You can also say

あかいほんはこれです

The red book is this.

Conclusion

I suspect that the there is a typo in your rule two. It should perhaps read

2. Adjective (い-adj or な-adj) Noun です

Notice the omission of the particle は.