Editing Tip: Proper Use of the Term 'Both'

The term both is commonly used in technical writing to indicate similarity between samples, datasets, or values. However, the dictionary definition of 'both' — “one and the other” — does little to clarify the meaning or proper use of this word. Furthermore, 'both' can be used as either a pronoun or a conjunction, and each of these contexts has its own grammatical rules. As a result, there is often confusion about how to properly use this term in technical writing. This post outlines a few simple rules governing the use of both.

'Both' as a pronoun

As a pronoun, 'both' indicates that two items are being discussed and is therefore used in place of the phrase “the two.” The use of 'both' to discuss three or more entities is grammatically incorrect.

• Both samples were measured. (i.e., The two samples were measured.)
• There were two outliers, and we removed both.

'Both' as a conjunction

As a conjunction, 'both' should only be used with 'and'; its use with other conjunctive phrases (e.g., “as well as” and “along with”) is not preferred. The pairing of 'both' with 'and' forms a grammatical construct known as a correlative conjunction (other examples of correlative conjunctions are “either...or” and “not only...but also”).

In the examples below, “both...and” is used as a conjunction relating two nouns, two adjectives, and two verbs, respectively.

• Both measurement A and measurement B had a value of 1.
• The assay was both simple and rapid.
• We both mixed and heated the sample.

Use with the phrase "the same"

Furthermore, as a conjunction, 'both' emphasizes that the two entities being discussed (whether nouns, verbs, or adjectives) are included equally. Therefore, the use of the term “the same” with 'both' is often redundant. You can drop one of these terms to make your writing more concise:

• Both measurement A and measurement B had the same value. (Incorrect)
• Measurement A and measurement B had the same value; both measurement A and measurement B had a value of one. (Correct)

In contrast, the use of “the same” is acceptable when using 'both' as a pronoun.

• Both measurements had the same value.
• Both trials had the same number of participants.
• The same conditions were used for both samples.

We hope that these few simple rules and examples will help to guide you in your use of the term both. If you have any comments or questions, please email us at [email protected]. Best wishes!