One of the most common tips for good scientific writing is to keep your sentences short. This is good advice because short sentences are usually easier to understand. However, if you only use short sentences your reader will struggle. Why? Consider this example:

PI3K-Akt signalling regulates cell proliferation. Akt kinase is at the centre of this pathway. It interacts with a variety of proteins. Akt is overexpressed in almost 80% of tumours. However, it is not a suitable target for cancer treatment. Inhibiting Akt has serious clinical side effects. Akt-interacting proteins regulate Akt kinase activity. They are potential targets for cancer therapy.

Although every sentence is short and easy to understand by itself, the text as a whole is very difficult to read. It’s rather like being in a car and jerking along rather than driving smoothly down the road. The problem is that the writing lacks rhythm. This makes it harder for the reader to understand how your ideas flow together. We can solve this problem by varying the length of our sentences:

PI3K-Akt signalling regulates cell proliferation. At the centre of this signalling pathway is Akt kinase, which interacts with a variety of proteins. Although Akt is overexpressed in almost 80% of tumours, it is not a suitable target for cancer treatment because inhibiting Akt has serious clinical side effects. Akt-interacting proteins can regulate Akt kinase activity and have emerged as potential targets for cancer therapy.

That’s much better. By using a combination of short and long sentences, we have made the text more interesting and easier to read. This dispels a common myth in research writing: that longer sentences are bad and should be avoided. What is important is that we use longer sentences where they are helpful and that we write longer sentences that are clear and easy to read. In this blog post, I explain when to use longer sentences in your research paper and how to make sure these longer sentences are easy to understand.

So where should you use short sentences and where should you use long sentences in your paper? That depends on whether you are making a key point or presenting information that supports a key point. Shorter sentences are a great way to draw your reader’s attention to important points while longer sentences are ideal for delivering supporting information. Let’s consider an example:

The RAS-RAF-MEK-ERK pathway is an evolutionarily conserved signalling cascade that is tightly controlled by multiple feedback loops to regulate cell proliferation, cell growth, and homeostasis under normal physiological conditions. Components of this pathway are frequently mutated in cancer.

Here, we start off with a long sentence that gives the reader important background information about the ERK signalling pathway. This long sentence speeds the reader up, moving them along towards the next full stop where they can finally pause and take a break. Then comes a short sentence that stops the reader in their tracks: Components of this pathway are frequently mutated in cancer. This sudden change in tempo immediately draws the reader’s attention to the information in that final sentence.

So, when writing, consider what your key points are. Use shorter sentences to emphasize these key points and use longer sentences to support these points with important details and create rhythm. It is often effective to have a short topic sentence at the start of a paragraph that draws the reader’s attention to the topic under discussion, or a short snappy sentence at the end of the paragraph that emphasizes the concluding comment.

A common problem with longer sentences is that they contain lots of information and can be difficult to understand. A useful tip is to start the sentence with the most important information and then follow this with a longer supporting clause that gives all the extra details. This way, the reader knows upfront what the main message is, making it much easier for them to absorb the additional information. Consider this example:

In patients older than 55 years and with a BMI higher than 25, colorectal liver metastasis, hepatocellular carcinoma, and cholangiocarcinoma were the most common indications for liver surgery.

This sentence is difficult to understand because the reader has to wait until the end to find out what we are talking about (common indications for liver surgery). Putting this information at the beginning of the sentence makes a big difference, without having to shorten the sentence:

The most common indications for liver surgery were colorectal liver metastasis, hepatocellular carcinoma, and cholangiocarcinoma in patients older than 55 years and with a BMI higher than 25.

This tip is particularly useful in the Results section when you are presenting long lists of variables with values and statistics. Instead of breaking the long list down into shorter sentences, tell the reader upfront what you are presenting. This will make the information that follows easy to absorb. Consider the following sentence:

Increased age (OR for 10-year increase = 0.83, 95% CI: 0.73–0.96, P= 0.009), obesity (OR = 0.25, 95% CI: 0.16–0.37, P < 0.001), biliodigestive anastomosis (OR = 0.27, 95% CI: 0.19–0.40, P < 0.001), and concomitant portal vein resection (OR = 0.49, 95% CI: 0.28–0.87, P = 0.014) were independent predictors of negative outcomes after major liver resection.

This sentence is difficult to understand because the reader has to keep four different variables in mind plus their odds ratios, confidence intervals, and P values before finding out what these variables are. Simply putting that information right at the start immediately makes the sentence easy to follow, despite all the variables and values:

Independent predictors of negative outcomes after major liver resection were increased age (OR for 10-year increase = 0.83, 95% CI: 0.73–0.96, P= 0.009), obesity (OR = 0.25, 95% CI: 0.16–0.37, P < 0.001), biliodigestive anastomosis (OR = 0.27, 95% CI: 0.19–0.40, P < 0.001), and concomitant portal vein resection (OR = 0.49, 95% CI: 0.28–0.87, P = 0.014).

Punctuation is another useful tool for creating rhythm in your writing as it tells your reader when to speed up and when to slow down. For example, you can indicate a short pause with a comma (,) or a longer pause with a semicolon (;). You can also direct your reader to information that follows with a colon (:) or separate parenthetical phrases with an en dash (–) or an em dash (—). For more specific guidance on punctuation, check out my earlier blog post.

Just like music, writing has its own tempo that determines whether we read slowly or quickly. Using the tips outlined in this article to vary the tempo of your writing will make your research paper more interesting and easier to read.

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.