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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

affect/effect/impact

Do not confuse the words affect, effect, and impact, each of which can be used both as a verb and as a noun. Avoid incorrectly using impact as a verb in place of affect or as a noun in place of effect.

Affect as a verb means "to influence."


The temperature affects the growth rate of the bacterial sample.

Affect as a noun has a specialized meaning in medicine and psychology, referring to moods and feeling as distinct from thoughts or knowledge.


Dua (1989) constructed the Thoughts and Real-Life Experience Scale (THARL) to assess the degree of positive and negative affect experienced by people as a result of their thoughts and day-to-day interactions.

--J. K. Dua, "The Role of Negative Affect and Positive Affect in Stress, Depression, Self-Esteem, Assertiveness, Type A Behaviors, Psychological Health, and Physical Health," Genet Psychological Monographs


Effect as a verb means "to bring about, to produce," or to "accomplish something."


The temperature reversal effected a major slowdown in the bacterial growth rate.

Effect as a noun means "result."


Increased bacterial growth rate was one major effect of the rise in pond temperature.

Impact as a verb means "strike with a blow" or "to pack firmly together."


The wisdom tooth impacted the molar.

Impact as a noun means "a collision."


The constant impact of the two gear mechanisms on each other eventually produced metal fatigue in several sprockets.


Do not use impact as a verb in place of "to affect."


Weak

The temperature impacts the growth rate of the bacterial sample.

Improved

The temperature affects the growth rate of the bacterial sample.


Do not use impact as a noun in place of "effect."


Weak

The release of hydrocarbons has had a significant impact on the depth of the ozone layer.

Improved

The release of hydrocarbons has had a significant effect on the depth of the ozone layer.


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