These adjectives beginning with a- are only used in the predicate (after a linking verb such as be, feel, look or seem) and never before the noun:
|The baby is asleep.||NOT The asleep baby....|
|The house is ablaze.||NOT The ablaze house....|
1 Aloof is used before the noun: an aloof person
2A few of the other a-adjectives are sometimes used before the noun if they are used with a modifier: the half-asleep man, the wide-awake child, the very ashamed student
But the basic rule is:
Do not use these adjectives before a noun.
NOTE: Other adjectives beginning with a- such as abominable, assertive, attentive, etc. are used before and after the noun and are not referred to as a-adjectives.
NOTE FOR TEACHERS:
Originally, the a-adjectives were formed from the old English word "a," which was a reduced form of the preposition "on"; it meant "on," "in," "into," "to," "toward." It was used with a noun to form a prepositional phrase and was used as a predicate adjective or an adverbial. (Random House Webster's Unabridged Dictionary v. 3.0).
Since these adjectives were originally prepositional phrases, they were used only after the noun. The "a" element eventually became fused to the noun forming the so-called a-adjectives. That is why they are used only after a noun today. These adjectives are marked with an asterisk (*).
The house is on fire. → The house is afire.
I have included some other adjectives in the list that begin with "a" but are not etymologically related to the Old English "a" meaning "on." These are included because they are used after the noun like the original a-adjectives and because they are included in other lists of a-adjectives that you might encounter.
For a linguistic paper on a-adjectives, see A-adjectives (asleep etc.) in postnominal position.