Authors often wonder about how to choose the proper verb tense when writing up a scientific paper. In some cases, the correct choice of tense is fairly straightforward. In many cases, however, there are several options, and the “correct” choice is simply a matter of convention. What verb tense should you choose, and in which particular cases?
First, some background about the verb tense discussed below. In general terms, the tense of a verb reflects the timing of the action:
- The past tense indicates that an action already occurred
- The present tense indicates that the action is currently occurring
- The future tense indicates that the event has not yet occurred
Verbs can also be conjugated into a past, present, or future perfect tense, in which the action is defined relative to another point in time (see examples below).
For many journals, the manuscript title does not need to be a complete sentence, and no verb is necessary. In cases where a complete sentence is appropriate, use the simple present tense to describe a conclusion that the manuscript supports (e.g., “Gene X is required for intestinal cell differentiation” or “Frameshift mutations in gene X cause abnormal notochord development in zebrafish”).
The introduction often includes several verb tenses, each providing a different context for the statement that it accompanies. First, when stating a fact that is widely accepted, the present tense is appropriate. Examples of such a statement include “DNA is composed of four nucleotides” or “trypanosomes exhibit global trans-splicing of RNA transcripts.” Use of the present tense signifies that the statement reflects the current understanding of the matter at hand.
Most introductions also include references to previous research. When referring to a previous study with results that are still relevant, use the present perfect tense (a form of the verb ‘have' plus a past participle, such as “have shown” or “has been shown”). This tense demonstrates that the action occurred in the past but still applies in the present. Phrases like “Johnson et al. have shown that gene X is part of an operon” or “unusual glycosylation events have been observed in these cells” are appropriate because the research or observation was made in the past, but the results are still valid. This tense is also used when the event began in the past but continues in the present (“patients with XYZ syndrome have been surveyed for the past ten years").
Please note that the present tense is used when a specific result, figure, or paper is the subject of a sentence. Like a movie or book, published research is still available for readers to examine, and a paper therefore continues to express its conclusions. Examples of statements about previous research using the present tense include “the results of their study indicate that the drug is highly effective” or “a landmark paper from Smith's lab describes the discovery of this new organelle.”
In some other parts of an introduction, the past tense is needed. When referring specifically to the methods used in a previous paper, the past tense is best. For example, it is correct to say “Smith and Anderson sampled 96 swamps and found 156 distinct dragonfly species” or “gene X was first cloned into a shuttle vector in 2003.” Likewise, statements that are no longer considered true should remain in the past tense: for instance, “bacteria were believed to lack introns” or “early physicists thought that electrons traveled in defined orbits.” At times, a combination of tenses is necessary: “Robert Corey suggested [past] that DNA contained three helices, but subsequent work has proved [present perfect] the existence of a double-helix structure.”
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