When Did It Happen?

In English, there are three main tenses: past, present, and future. These three tenses have simple and perfect forms, which allow you to say when something happened and whether the process is ongoing or finished:

|||Simple|||Perfect

Past|||I investigated|||I had investigated

Present|||I investigate|||I have investigated

Future|||I will investigate|||I will have investigated

Many non-native English-speaking scientists don't use these tenses correctly in their research papers. But proper use of verb tense is important for readability. In this blog post, I explain when to use which tense and point out common mistakes to help you get it right in your next paper.

The main tenses used in research writing are the simple past, simple present, and past perfect.

The simple present is used in the Introduction section of your research paper to describe something that is known to be true and will (probably) not change. For example:

DNA is composed of two chains that coil around each other to form a double helix.

Although the DNA double helix was discovered in the past, using the simple past tense here (DNA was composed of…) would be misleading, as it would suggest that DNA did have a double helix structure but no longer does.

You can also use the simple present tense to state the main aim of your paper:

In this study, we investigate the effect of childhood trauma on obesity in adulthood

or in your Conclusions to describe what you have shown (i.e., what is now known thanks to your work):

In this paper, we show that childhood trauma is associated with obesity in adulthood.

You can also use the simple present to refer to published findings without mentioning the author’s name:

Donor age affects graft survival following liver transplantation

or to emphasize that a published finding is still valid and relevant:

The surgical method reported by Bloggs et al. remains the most accepted approach in the field.

And you should use the simple present tense to refer to tables and figures when describing your results:

Table 1 shows the patient characteristics at recruitment.

The present perfect is a present tense that refers to something that happened in the past. Confused? Don’t be – the present perfect tense has a very clear job that distinguishes it from the past tense: to stress the present importance of a past event. Take a look at these sentences:

A national emergency was declared (use of the simple past suggests that a national emergency was declared and that the emergency is now resolved – i.e., it is no longer relevant to the present).

A national emergency has been declared (use of the present perfect suggests that a national emergency was declared and that the emergency is still happening – i.e., it is still relevant to the present).

In research writing, you can use this tense to describe something that has been done that is important or relevant to your present study. For example, you can use the present perfect tense to emphasize the relevance of a cited study to your own work:

A recent study has shown that childhood trauma significantly affects lifestyle choices.

The present perfect tense can also connect what is known with whatever gap in the current knowledge your planned study will fill. For example:

Although childhood trauma has been linked to lifestyle choices later in life, the effect of childhood trauma on obesity is unknown.

You can also use the present perfect tense (or the simple present as explained earlier) to describe what your results show:

In this study, we have shown that childhood trauma is linked to obesity in later life.

Non-native English-speaking scientists often overuse the perfect present tense – probably because they are translating directly from their own language. In German, for example, the present perfect tense is often used for normal past tense statements. For example:

Wir haben Blutproben von Patienten gesammelt (English translation: we have collected blood samples from patients).

Although this is perfectly fine in German, using the perfect present tense in this way is incorrect in English because we are describing something that has already happened and has no relevance to the present:

We collected blood samples from patients (simple past)

should be used instead.

This tense is used to refer to a completed action. In research writing, it should be used to describe your methods and findings. For example:

Creatinine levels were measured in the serum samples (Correct description of a method)

Creatinine levels were higher in older patients (Correct description of a result).

The simple past tense should also be used to report published findings from a specific study:

Bloggs et al. described how to culture cortical neurons from mouse embryonic tissue.

It is sometimes necessary to switch tenses in a sentence. For example:

A 1998 study in the Lancet showed a link between the MMR vaccine and autism in children, but this claim is undeniably and irresponsibly false.

This sentence uses the simple past tense (a study showed) followed by the simple present (this claim is) to indicate that a past belief has been disproven and has now changed.

A common mistake in research writing is to switch tenses when discussing one topic in a particular point in time. For example:

Although the rate of postoperative complications decreased in the experimental group, the five-year mortality increases (Incorrect).

In this sentence, both the simple past (postoperative complications decreased) and simple present (overall mortality increases) are used to describe results that were found at the same time – which confuses the reader. To clarify that both events occurred in the past, we need to change the simple present to the simple past:

Although the rate of postoperative complications decreased in the experimental group, the five-year mortality increased (Correct).

Each of the six tenses described above can also be used in a continuous form to show that something is ongoing:

|||Continuous|||Perfect continuous

Past|||I was investigating|||I had been investigating

Present|||I am investigating|||I have been investigating

Future|||I will be investigating|||I will have been investigating

In a scientific paper, you usually don’t need to indicate that something is ongoing, so you don’t need to use the continuous tenses. They are usually best avoided because they clutter up your paper with unnecessary use of the verb ‘to be’. For example:

We measured creatinine levels in patient urine (past simple)

is much more concise and easier to read than

We were measuring creatinine levels in patient urine (past continuous).

Tenses explain the time framework of your research story. The guidelines outlined in this blog post will help you to use tenses correctly in your next research paper so that your reader knows exactly what happened and when.

Help your reader by keeping time

Claire Bacon is a former research scientist with professional qualifications in copyediting and medical editing. She edits scientific research papers and teaches courses on scientific writing.