Scientific writing often involves measurements and units such as milliliters (ml) or microns (µm). Measured quantities involving these units are often found in tables or parentheses, and not always within the text of a sentence. However, when a measured amount (e.g., 500 ml) is the subject of a sentence or clause, the choice of verb to agree with the measurement presents a unique situation in academic English writing.
When a measurement is being described in a sentence, that quantity takes a singular verb form. In such cases, the entire quantity is thought of as a single entity that should be considered together, not separately. See the following examples, in which the entire sample was added or tested at a single time:
- In total, 10 g of tissue was tested. (NOT: 10 g of tissue were tested)
- Five milliliters of solvent was added to the mixture. (NOT: Five milliliters were added)
A plural verb is appropriate when items should be considered individually (e.g., "Ten mice underwent surgery"). In this example, surgery was performed on ten mice, one at a time, so a plural verb is correct.
Last, percentages can fall into either category: a collection that should be treated as a single entity (singular verb) or a group of individuals that should be treated separately (plural verb). For example:
- In total, 30% of the study duration was spent on the follow-up testing.
Here, the duration (an amount of time) can be thought of as a single block, not as countable units.
- Twenty percent of the participants were assigned to the experimental condition.
In this example, each participant was assigned to experimental or control conditions, and the number of individual patients assigned to the experimental group constituted 20% of the total patient sample.
English grammar is sometimes tricky, and academic writing often adds new confusing conventions. We hope that this post has helped clear up the use of singular or plural verbs with measured quantities. As always, please email us if you have questions.