Grammar

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Last modified: 2026-06-22 06:24:47 (UTC)

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Clear grammar removes friction between your ideas and your reader. This chapter collects a few grammatical habits that consistently make scientific writing easier to read.

1 Relative pronouns

Relative pronouns introduce a clause that describes a preceding noun. The relative pronouns are:

  • that
  • which
  • who
  • whom
  • whose

Two habits make these clauses easier to read: choosing between that and which correctly, and keeping the relative pronoun rather than dropping it.

1.1 Restrictive vs. non-restrictive clauses: that vs. which

Use that for a restrictive clause — one that identifies which thing you mean, and that cannot be removed without changing the meaning of the sentence. Use which, set off by commas, for a non-restrictive clause — one that adds information the reader does not need in order to know which thing you mean.

Example 1 (Restrictive clause (that))  

The dataset that we collected in 2023 contains 4,000 records.

The clause “that we collected in 2023” tells the reader which dataset we mean. Removing it changes the meaning, so the clause is restrictive and takes that with no comma.

Example 2 (Non-restrictive clause (which))  

Our 2023 dataset, which contains 4,000 records, is publicly available.

The clause “which contains 4,000 records” adds a detail, but the reader already knows which dataset we mean. The clause is non-restrictive, so it takes which and is set off by commas.

A quick test: if you can drop the clause without changing which thing you are describing, use which and commas; otherwise, use that.

1.2 Do not omit relative pronouns

English lets you drop a relative pronoun in some sentences, but keeping it makes the structure of the sentence explicit and easier to parse on the first read. Prefer to keep that, which, or who, even when the grammar would let you drop it.

Example 3 (Restoring an omitted relative pronoun)  

❌ This body of work laid the methodological groundwork I now apply to enteric fever.

✅ This body of work laid the methodological groundwork that I now apply to enteric fever.

The word “that” signals immediately that a describing clause is beginning, so the reader does not briefly misread “the methodological groundwork I” as a single phrase and then have to backtrack.

2 Demonstrative pronouns

There are four demonstrative words:

  • this
  • that
  • these
  • those

They can serve two roles. As adjectives, they modify a noun: “this result”, “those samples”. As standalone pronouns, they replace a noun: “This shows…”, “That means…”.

When a demonstrative stands alone as a pronoun, the reader has to search backward for its referent — and often the referent is a whole preceding clause rather than a single noun, which leaves the reference ambiguous. Prefer to follow a demonstrative with the noun it points to, so the reference is explicit.

Example 4 (Naming the referent)  

❌ The model overfit the training data. This poses a problem for deployment.

✅ The model overfit the training data. This overfitting poses a problem for deployment.

Adding the noun “overfitting” states exactly what “this” refers to, instead of leaving the reader to infer it.

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