Did it? Does it? Will it? – Verb tense in scientific writing

Have you ever had trouble choosing the correct verb tense for your research paper? If you answered “Yes”, read on to find out how to choose verb tense for impactful scientific writing.

Format of a scientific paper

Most scientific research papers follow the Introduction, Methods (Materials, Experimental), Results, and Discussion/Conclusion (IMRaD) format. Each section of the paper serves a distinct purpose.

Introduction: state of knowledge that led to hypothesis
Methods: procedures used to test hypothesis
Results: findings obtained by the experiments
Discussion: summary of decisive results and tentative conclusions

Because each section has a different purpose for the whole paper, it is common that the verb tense is different within each section and between sections.

Introduction

In the introduction, you must create context for the hypothesis or problem you are trying to solve by describing the current state of knowledge and background information. You do this by citing the relevant literature. When citing the literature, you should use the past tense and the present tense. Use the past tense to describe what was done in the research. Use the present tense to describe what was found in the research.

For example,
“Smith and Jones studied the stability of nitrogen-substituted aziridines. They found that these small nitrogen containing heterocycles are acid sensitive and open under acidic conditions.”

I used past tense to describe what they did in the study, but present tense when describing their results. The results are discussed in the present tense because they touch the present, that is, they remain true in the present (unless proved otherwise) and are current knowledge. Examples of this include characteristics, properties, and applications of materials; calculations with a specific tool and parameters; and techniques that improve a process.

In the last part of the introduction, the past, present, and even future, tenses can be used together.

“Here, we studied nitrogen-substituted aziridines to screen how nitrogen substitution changes the stability of the heterocycle under acidic conditions which will broaden its applications as an amine synthon.”

Methods/Materials/Experiments

Although this section may not be the most interesting to write, it is perhaps the easiest. Simply use the past tense in this section to describe what you did. All experiments for the paper were performed in the past. You or your colleagues did these experiments. Work may continue on this project with follow-up experiments, but for this paper, now, the experiments are finished. If a reviewer asks you to include more experimentation in the paper, you will still present it in the past tense in the final draft.

Remember, the procedures used to test your stated hypothesis or problem are always in the past relative to reporting and discussing the results.

“The reaction mixture was stirred at 100 °C for 10 h.” Simple past tense for the win!

Results

The results section can use more than one tense, which often leads to confusion about what tense is most appropriate in specific situations.

Typically, figures and tables are referred to in the present tense:

“Figure 1 shows…”
“Table 1 contains the conditions screened…”

Although this may seem odd because the results were obtained in the past, your published paper is always read in the present. Even if the experiments were faulty and another paper shows that the results were wrong, or there is a retraction or correction, the figures in this iteration of the paper will always show these results.

However, it gets complicated when the results within the table or figure are discussed. You can choose either the present tense or the past tense.

“Figure 1 shows that as the reaction temperature decreased the reaction rate decreased.”

The past tense in the above sentence is correct. But the following can also be correct.

“Figure 1 shows that as the reaction temperature decreases the reaction rate decreases.”

So which one should you choose? Both are correct, but I prefer the present tense in this case. I try to keep in mind that under these specific conditions, anyone trying to repeat this experiment should expect the same results.

Thus, the result —obtained in the past by experimentation—touches and continues into the present (repeatable system or characteristic of the system) and is most appropriately discussed in the present tense. The is a specific tense for these types of situations called the progressive tense, but it isn’t needed here. For a more in-depth discussion of the progressive tenses see CMOS.

Here's another example, DFT calculations of this system, with this method will always give the same result.  

Discussion

Sometimes the discussion section is separate from the results, or it may be included within the results section. Either way, I think it makes the most sense for this material to be in the present tense. Think of these questions when writing the discussion.

How does the system act when probed this way?

What are the properties of the system (catalyst, molecule)?

• What are your results?
  
• What do the results mean?
• What is their impact?
  
• 
  

What if I use the past tense here?

• What were your results?
• What did the results mean?
• What was their impact?
  
• 
  

The past tense in the questions above give the sense that the knowledge you gained isn’t current. It’s already past. If the knowledge isn’t current then your audience wonder why they should care about your conclusions.
Remember that your conclusions and interpretations of the data are new. Put them in the present tense for the most powerful impact. For example,
“We ascribe the slower reaction rate to a lack of sufficient energy in the system.”

If the sentence is “We ascribed the slower reaction rate…”, a reader might ask, “So how did you fix it?”

Conclusions

As in the Introduction, Results, and Discussion, the conclusion section also needs to be written in more than one tense.

Use the past tense to summarize the study. “We studied the effects of substitution on aziridine stability.”

Use the present tense to summarize the results. “Substitution of the aziridine nitrogen changes its stability.”
“Here, we show…”

• Materials have these properties and characteristics
• The reaction behaves this way under these conditions
• Our system solves this problem
  

Use the future tense to describe the results’ impact or meaning. “Our findings will broaden the use of aziridines as amine synthons.”

Still Unsure?

Scientific writing is challenging, even for a seasoned academic. When writing your research paper, remember what the intent of each sentence is and you’ll be able to easily chose the best verb tense.

Do you have trouble with verb tenses in scientific writing? Drop me a message on LinkedIn and we can chat about it.