of', 'opens the door to', are not themselves particularly noisy phrases; but writers who indulge in them generally end by being noisy.
Unintentional metaphor is the source, too, of most actual blunders. Every one is on his guard when his metaphor is intentional; the nonsense that is talked about mixed metaphor, and the celebrity of one or two genuine instances of it that come down to us from the eighteenth century, have had that good effect. There are few obvious faults a novice is more afraid of committing than this of mixed metaphor. His fears are often groundless; many a sentence that might have stood has been altered from a misconception of what mixed metaphor really is. The following points should be observed.
1. If only one of the metaphors is a live one, the confusion is not a confusion for practical purposes.
2. Confusion can only exist between metaphors that are grammatically inseparable; parallel metaphors between which there is no grammatical dependence cannot result in confusion. The novice must beware, however, of being misled either by punctuation or by a parallelism that does not secure grammatical independence. Thus, no amount of punctuation can save the time-honoured example 'I smell a rat: I see him hovering in the air:... I will nip him in the bud'. Him is inseparable from the later metaphors, and refers to the rat. But there is no confusion in the following passage; any one of the metaphors can be removed without affecting the grammar:
This royal throne of kings, this sceptred isle,
This earth of majesty, this seat of Mars,...
This fortress built by Nature for herself...
This happy breed of men, this little world,
This precious stone set in the silver sea,...
This blessed plot, this earth, this realm, this England,
This nurse, this teeming womb of royal kings,...
3. Metaphor within metaphor is dangerous. Here there is a grammatical dependence between the metaphors, and if the
