A good deal depends on the current of breath with which the [h] is uttered. In standard English the current does not keep on growing in volume until the vowel is sounded; it distinctly diminishes before the vowel appears. This may be graphically represented by the signs [<h>].
If the current of breath does not diminish in this way, but starts weakly and does not reach its maximum force until the vowel is reached, the ear does not receive the impression of a distinct [h]. This sound may be written [h<] or simply [<]. This (the "soft breath") precedes initial vowels in standard English; it is the sound which in cockney speech commonly represents the more distinct [<h>]; those who use it are said to "drop their h's." Conscious of the defect, they often prefix a full, even an exaggerated [h] to words which have no h. It need hardly be said that carelessness in the use of h is not to be tolerated. It is interesting to note that no h is ever dropped in the speech of Americans, except in the weak forms of he, him, her.
[h] occurs in standard English only before stressed vowels. Initial h before unstressed vowels is only pronounced when preceded by a pause.
Notice that:
1. Written h is not pronounced in heir, honest, honour, hour, and words derived from these.
It is now pronounced in standard English in herb, hospital, humble, humour (a fair number of educated speakers still pronounce this word without [h]).
2. It is regarded as correct to say a history, but an historical novel; a habit, but an habitual action; many, however, pronounce the h in both cases.
3. Certain words drop the h when they occur in an unstressed position in the sentence; this is a regular feature of standard colloquial speech, and does not convey the slightest suggestion of vulgarity. It must be recognised that such words have two forms, weak and strong, according as they are used without or with emphasis. Compare the following sentences: