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The Mayfield Handbook of Technical & Scientific Writing
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Usage Glossary: A B C D E F G H I K L M N O P Q R S T U V W Y


Have is a verb. As an auxiliary verb, it often follows modal auxiliaries such as would, should and must.

The rocket would have been sent up yesterday, but the weather was bad.

Of is a preposition. It is almost always preceded by a noun or a main verb and followed by a noun phrase.

The delay of the rocket firing was due to bad weather.

In designing the rocket, the engineers thought of everything but the weather.

Never use of after a modal auxiliary; use have.


We must of made a mistake.


We must have made a mistake.

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