该语法书的说法是准确的，也是有依据的。比如英国著名语法学家夸克(R. Quirk)等人在其编著的《英语语法大全》(A Comprehensive Grammar of the EnglishLanguage,Longman,1985)的第7.11节有如下说明(注意最后一段的说明)：

7.11 A-adjectives vary as to whether they can be attributive. Most a-adjectives are only marginally acceptable in attributive function, unless they are premodified（至于a-形容词能否作定语用，则视情况而异。大多数a-形容词，除非它们被前置修饰语修饰，只勉强能起定语作用）：

? an afraid look

? an alive eye

Aloof and alert, however, are fully acceptable in attributive function, eg（然而，aloof和alert完全可以起定语作用。例如）：

an aloof character

an alert manner

Most a-adjectives can occur attributively when they are modified（大多数a-形容词，在它们有修饰语的时候，可以起定语作用）：

a somewhat afraid soldier

the fast asleep children

a really alive / lively student

the wide awake patient