How To Write

Based on: Heard (2016).


You may have noticed that scientific articles use different tenses (times) in different sections. Which tense should you use in which part? Often, that depends on context and partly on taste, but there are some general rules of thumb. For example, it makes sense that most of the Materials and Methods section is written in past tense, because it simply describes the work you carried out (in the past) to come to your results. In other sections, like the Discussion, the answer is less clear cut.


Here, we will go through the main components of IMRaD and review the most commonly used tenses in them. For sake of clarity, let’s start with a quick review of time tenses. There are not three (past, present, future), but in fact 12 tenses, each with their own implication (Table 1).


Table 1. The twelve time tenses in English.
 simple ~  ~ progressive  ~ perfect  ~ perfect progressive
Past  I wrote  I was writing  I had written  I had been writing
Present  I write  I am writing  I have written  I have been writing
Future  I will write  I will be writing  I will have written  I will have been writing
Implication Duration is not important Indicates ongoing process through time Indicates a completed action Combining the passage of time and completion of an action.

The Introduction uses a mix of tenses, each tense having their own role. The past perfect is often used to refer to research over time, whilst the present tense is used for current understanding.



1) The effects of microplastics in aquatic food webs have been studied increasingly over the last years.

2) The global climate is changing.

One can even use the future tense, for example when identifying a knowledge gap (often, this knowledge gap is conveniently filled by the current study):

3) A better understanding of the effects of medical waste in fresh water on fish behavior will allow the development of better management guidelines.

Something that will improve your scientific writing is knowing when to use passive and active voice in your text. Although personal preferences are debatable on this topic, we encourage the general rule to use the active voice as much as possible, but that passive voice should be used when you have reason to do so.

Active voice emphasizes the subject doing an action: the actor (subject) comes before the verb, and the recipient of the action (object) comes after.

The passive voice emphasizes the object receiving the action: the object comes before the verb, and the subject (if mentioned at all) comes after.

 Active voice  Passive voice
 A large number of invertebrates and vertebrates inhabit the ocean.  The ocean is inhabited by a large number of invertebrates and vertebrates.
 Scientists classify sharks as elasmobranchs.  Sharks are classified as elasmobranchs.
 We measured the fish’ total length (cm).  Fish total length (cm) was measured.

The active voice will usually make your sentences shorter and easier to read. It also tends to make your sentences more engaging, vivid and honest. However, there are times when the passive voice is preferable (see below). Some will also argue that it can be nice to vary the voice a bit to make your language less monotonous.

If you are going to publish your work: keep in mind that some journals might prefer more use of passive or more use of active voice. Read articles from the journals where you want to publish to see what they prefer.

When to use the passive voice

  • 1. When the subject is unimportant, unknown or obvious

Passive voice example: Subsamples are often preferred when the total size of the sampled data is too large for efficient data collection.

In this example, the subject is left out. Technically, the subject here would be the research community as a whole, preferring to take subsamples. However we don’t need to mention that specifically, because that is obvious and/or unimportant in this case.

  • 2. When the object or action itself is more important than the agent

Passive voice example: Fish total length was measured to the nearest cm.

Passive voice is commonly used in the materials and methods. Here, the one doing the action (the researcher(s)) is not important, but the action itself and the recipient of the action are.

  • 3. When the object is the topic of the sentence

Passive voice example: Ocean surface temperatures are monitored all over the world and have been found to have risen over the past decades.

Who monitors these temperatures (researchers) are not the topic of the sentence, the temperatures are.

  • 4. When the subject is too complex

Active voice example: Atlantic cod, redfish, killer whales, harp seals and several other piscivore predators among various taxa predate on herring.

Passive voice example: Herring is predated on by Atlantic cod, redfish, killer whales, harp seals and several other piscivore predators among various taxa.  

Here, the subject is a long list of species/taxa and the verb is far out in the sentence. This makes it difficult to follow. The sentence becomes clearer and easier to understand by using the passive voice.

Paragraph structure

Paragraphs help communicate your story to the reader by separating different ideas. Ideally, all information within a paragraph revolves around the same topic. All paragraphs are built up in three main parts: a topic sentence, supporting sentences and a concluding sentence. The topic sentence sets the theme of your paragraph and is commonly the first or second sentence. It introduces the main idea of the paragraph that the following supporting sentences will elaborate on. Supporting sentences elaborate on the main idea presented in the topic sentence of your paragraph. The concluding sentences give a conclusion to your paragraph based on your supporting sentences.


Transitions within a paragraph

The information in a paragraph revolves around the same topic introduced in the topic sentence, which already improves readability. However, good transitions between sentences are important to add flow to your text, and lead the reader in the right direction. Compare these two examples:

Example 1
Paragraphs lacking transitions between sentences can be difficult to read. Paragraphs that have good transitions are often easier to read. Although the information might be the same, including well-picked transitions makes the text easier to process. It is important to make sure that your sentences are well connected to each other.

Example 2
Paragraphs lacking transitions between sentences can be difficult to read. In comparison, paragraphs that have good transitions are often easier to read. Although the information might be the same, including well-picked transitions makes the text easier to process. Therefore, it is important to make sure that your sentences are well connected to each other.

By using transition words and phrases in Example 2 it is easier to understand how the sentences relate to each other and it becomes easier to follow the author’s line of thought.


Transitions between paragraphs

Even though each of your paragraph should have their own theme and main idea, the paragraphs must still be connected to each other to ensure a nice flow to you scientific text. Transitions connects statements and ideas and making good transitions between paragraphs is crucial to aid the reader.

Ways to transition between paragraphs:

  • • By linking ideas. Try to arrange your paragraphs so that the idea of one paragraph can build off the one before.
  • • By using transition words and phrases. Sometimes you can also use transition words and phrases to transition between paragraphs (e.g. first, second, therefore, moreover, similarly), but make sure that these transitions do not result in the reader losing the overview of what the tropic of the paragraph is.
  • • By using similar words in the present paragraph compared to the prior you are also connecting them.

One way to proofread your paragraphs is to look at the last sentence of one and see how it connects to the first sentence of the next.

Be careful with the use of synonyms

In scientific writing the clarity of the text is what is most important. Therefore, you should be careful with the use of synonyms. These can cause unnecessary confusion. Try to use the same terms throughout your study to maintain clarity.
Use precise language

When describing numbers and amounts, try to use precise values when you can and include standard deviation or error bars when relevant. Avoid using vague terms like for example “a large number of” or “considerably less” - these can mean very different things depending on the topic.
The use of abbreviations

There is a difference between abbreviations that is more or less universally accepted and the ones related specifically for your study. Common abbreviations are for example units (meter = m., litres = l.), months (January = Jan, February = Feb) and some common terms (“and so forth” = etc., “for example” = e.g.).

In scientific studies, abbreviations can also be used to shorten down names of specific equipment or treatment types. Make sure to write the word in full the first time you use it (with the abbreviation in parentheses), and furthermore you can use the abbreviation throughout the rest of the text. If you are publishing your work: keep in mind that some journals only allow for a minimum of abbreviations. Read the guidelines of the journal carefully.