Pattern 1 : N be Aj3

"Food is good "

In the nine basic patterns the subject always occurs in the first N position. In pattern 1 the grammatical meaning of the subject is “that which is described” In each of the first three patterns the verb be has different meaning.
Here the meaning “may be described as”.
In pattern 1 the third term must be an adjective or adjectival :

“that food is poisonous”

You can test pattern 1 in simply way. It is capable of this expansion :

That food is good > that good food is very good.
That food is poisonous > that poisonous food is very poisonous.

If a sentence will not undergoe this expansion it belongs to some patterns other than pattern 1. for example :

“my mother is outside”

Grammatical meaning are also carried by morphological forms. For example the italicized morphemes that follow have grammatical meaning : boys, dreamed, sweetness. The concept of grammatical meanings ia a convenient one eventhough a sharp line between grammatical and lexical or dictionary meaning cannot always be drawn.

The foregoing pattern 1 does not work in all cases. Nor for that matter, does any grammatical rule of the test, unless it is accompanied by exception and qualifications.