**Where to introduce an acronym**

**Standard rule for introduction of an acronym**

The standard rule given by many journals, style guides, and editors for when to introduce an acronym or initialism is to introduce it at the first use of the full term. Thereafter, the acronym or initialism, without the full term, should be used instead. An acronym or initialism should not be used alone (without the full term) if it has not been explained to the reader in earlier text. This is the most efficient and straightforward approach. You’re probably quite familiar with this approach already, but let’s consider some applications of this rule. For a start, where is the full term first used in a paper? Is it in the abstract or is it in the Introduction or a later section? Actually, it’s in both.

The abstract is treated separately from the main text of the paper, as it is the first thing someone reads when conducting a literature review or otherwise searching for information. A person might choose to read only the abstract and not the accompanying full paper (for example, if it’s not in their field of interest), so the abstract must be able to stand alone, that is, it shouldn’t require the reader to know any extra information from the main text of the paper. Therefore, any acronyms and initialisms used in the abstract should be introduced there, in the abstract. For example, suppose that we have a paper with the following abstract:

Without initialism: “In this paper, an acoustic wave propagator approach is employed to investigate sound propagation around a barrier. The acoustic wave propagator is implemented using a Chebyshev polynomial expansion and a fast Fourier transform…”

Using the initialism ‘AWP’ for ‘acoustic wave propagator’, we can write this as:

With initialism: “In this paper, an acoustic wave propagator (AWP) approach is employed to investigate sound propagation around a barrier. The AWP is implemented using a Chebyshev polynomial expansion and a fast Fourier transform…”

Since “fast Fourier transform” is used only once and then not used again in this abstract, there’s no need to introduce the common initialism ‘FFT’ in the abstract.

The next place to introduce an acronym or initialism is in the main text of the paper, that is, the actual article from the Introduction to the Conclusion. I find that some authors will introduce their acronyms and initialisms in the abstract, but not in the main text of the paper. The thinking of these authors is probably that the reader has already read the abstract (usually presented on the same page). However, I don’t believe this is a useful approach. A reader may not necessarily return to the abstract, and the publisher might not print the abstract and main text on the same page. In the submission process, the abstract and main text might be sent to reviewers separately. Furthermore, it can aid discussion to reuse the full term, as I’ll discuss later. Therefore, it’s good practice, and requested by many style guides, to also introduce an acronym or initialism at the first use of the full term in the main text of the paper. Let’s look at how this works. Imagine that we’re introducing the initials ‘AWP’ for ‘acoustic wave propagator’ in the following passage:

Without initialisms: “They developed the acoustic wave propagator approach as an analogy to the quantum wave propagator, which was already in use by quantum physicists… Integrating Equation 3.8 with respect to time produces a formal solution for the state vector Φ(x, t), where exp(−(t−t0)H) is the acoustic wave propagator. By applying the acoustic wave propagator to the initial state vector, solutions for the sound pressure and particle velocity can be obtained at any time t. The acoustic wave propagator is defined as U = exp(−(t−t0)H).”

The first mention of the acoustic wave propagator is in the first sentence, so we write “They developed the acoustic wave propagator (AWP) approach.” After this initialism has been introduced, we can use the initialism in any or all of the following sentences:

With initialisms: “They developed the acoustic wave propagator (AWP) approach as an analogy to the quantum wave propagator, which was already in use by quantum physicists… Integrating Equation 3.8 with respect to time produces a formal solution for the state vector Φ(x, t), where exp(−(t−t0)H) is called the AWP. By applying the AWP to the initial state vector, solutions for the sound pressure and particle velocity can be obtained at any time t. The AWP is defined as U = exp(−(t−t0)H).”

The term “acoustic wave propagator” was mentioned four times in the first passage, so you can see how using the initialism instead made the second passage shorter and easier to read.

These are the standard rules for acronyms and initialisms: introduce them at the first use of the full term in the abstract and at the first use in the main text of the paper. Many journals specifically request this, and it should be thought of as the default approach for authors. However, there are a number of alternatives that should also be considered for a more refined approach. Nevertheless, one should always follow the submission requirements of a journal for a paper, or the guidelines of a university or department for a thesis, before applying one of these.

**Reintroduction of an acronym**

For the first alternative, it can be helpful to reintroduce an acronym or initialism in each section of a very long paper or in each chapter of a thesis or book. In a very long work, a reader may forget what an acronym or initialism originally meant, so the reminder is helpful. A reader may even skip sections or chapters if they’re not specific to their interest, so reintroducing an acronym or initialism helps to ensure they will come across the full meaning. As with the standard rule, the acronym or initialism should be introduced at the first use of the full term in the section or chapter. Continuing our worked example, suppose Chapter 2 of a thesis contains the following sentences:

- “Pan & Wang developed an acoustic wave propagator (AWP) and solved it using Chebyshev polynomial expansion… Peng et al. later adapted the AWP to investigate power flow and deformation effects in L-shaped plates…”
- “Following this formulation to solve an AWP, a general exponential operator can be expanded using Chebyshev polynomials…”
- “An alternative Chebyshev expansion was later introduced by Pan & Wang as an improvement on the previous method, for use in solving AWPs…”

The initialism AWP is introduced at the first use of ‘acoustic wave propagator’ in this chapter, and ‘AWP’ is used thereafter. Chapter 3 contains the example passage I used earlier:

- “Pan & Wang developed the acoustic wave propagator (AWP) approach as an analogy…”

Chapter 3 discusses the acoustic wave propagator in detail, so ‘AWP’ is reintroduced and is used frequently in this chapter. Later, Chapter 5 contains these two sentences:

- “This chapter shall concentrate on using the modified Chebyshev expansion of the acoustic wave propagator (AWP) to computationally model the propagation of sound from the noise source and its scattering around the barrier.”
- “In this chapter, an innovative wave-trapping noise barrier was modelled and compared to equivalent traditional noise barriers, using the modified Chebyshev expansion of the AWP to propagate noise around them.”

The term ‘acoustic wave propagator’ is only used twice in this chapter. The initialism ‘AWP’ is introduced at the first mention and used in the second. Next, in Chapter 6, which covers a quantum wave propagator instead, there is only one relevant sentence:

“The exponential operator will be expanded in much the same way as the acoustic wave propagator in Chapter 3, though with the following differences.”

Therefore, no abbreviation is required in this chapter.

Similarly, it is also helpful to reintroduce acronyms and initialisms in the conclusion, as a reminder to the reader. Some readers may skip ahead to the conclusion and may miss where an acronym or initialism was introduced, so reintroduction helps ensure it is explained to them. A conclusion section reiterates the main points of the paper, so reintroducing a key acronym or initialism can be seen as part of the revision of this information. Continuing the above example, in the conclusion, there are only two relevant sentences:

- “The project first examined an application of the Chebyshev polynomial expansion to the acoustic wave propagator (AWP).”
- “A potential application of the AWP solutions in the field of industrial noise barrier design was also presented.”

The initialism ‘AWP’ is reintroduced in the first sentence and used in the later sentence. This approach is useful in theses and very long papers, and even in papers of typical length. However, it probably won’t be necessary in very short papers, as a reader should be able to recall the full meaning or easily look back for it.

**Introduction of acronyms in letters and multi-part papers**

Speaking of very short papers, an article classed as a letter typically does not have an abstract or a conclusion. The standard rule applies: an acronym or initialism is introduced at the first mention of the full term in the letter, and it won’t need to be re-introduced at all.

On the other hand, multi-part papers are treated as completely separate papers when it comes to introducing the meanings of acronyms and initialisms. This is because a reader may read one part and not the other. The different parts of the paper may even be published in separate issues of a journal, and these could be weeks or months apart. Therefore, they should be treated as separate papers for the purposes of introducing acronyms and initialisms. If an acronym is introduced in the first paper, then it should also be introduced in the second paper.

**Late introduction of acronyms**

I’ve explained the standard rule and its applications, but you may prefer to introduce the acronym or initialism later in the discussion, and not at the first mention in the text. This can be more useful for discussion or explanation of a concept. For example, the first use of a term might occur in the Introduction, but it might only be briefly mentioned there. Instead, the concept might be properly defined or discussed in a later section. Let’s look again at one of the above examples:

- “Pan & Wang developed the acoustic wave propagator approach as an analogy to the quantum wave propagator, which was already in use by quantum physicists…”
- “Integrating Equation 3.8 with respect to time produces a formal solution for the state vector Φ(x, t), where exp(−(t−t0)H) is the acoustic wave propagator (AWP). By applying the AWP to the initial state vector, solutions for the sound pressure and particle velocity can be obtained at any time t. The AWP is defined as U = exp(−(t−t0)H).”

The first passage only briefly mentions an approach based on the acoustic wave propagator, while the second passage gives a formal definition of the acoustic wave propagator. Using the complete term in the second passage helps the reader to understand that this is a propagator function for the acoustic wave equation. It is also natural to define a concept using the full name, not merely an abbreviation that is only used as a shorthand for subsequent discussion. Introducing the acronym or initialism later thus makes the discussion more effective, and only slightly longer, compared to the standard approach.

**Table of abbreviations**

In addition, a few journals and thesis guidelines require authors to include a table of abbreviations and variables, including acronyms and initialisms. This is usually on the first page of the paper or in the first few pages of a thesis. A reader can consult this list to understand anything they come across and don’t understand or need a reminder for. Once an acronym or initialism is defined in a table of abbreviations, then it usually does not require definition at the first use of the term within the main text of the paper. However, an author may still wish to use one of the alternative approaches to the introduction of acronyms that I described above.

**Summary of approaches**

Let’s summarize the places where you may choose to introduce an acronym or initialism:

When to introduce | Why | Benefit |
---|---|---|

At the first use of the term in a body of text | This explains the meaning of the acronym or initialism to the reader immediately. All subsequent uses can be replaced by the acronym or initialism. | Most efficient |

At the first use of the term in the abstract | The abstract is treated independently from the paper. | Abstract can stand alone for readers |

At the first use of the term in the main text of a letter, paper, or thesis | The main text is treated independently from the abstract | Ease of understanding for readers |

At the first use of the term in each chapter of a book or thesis, or each section of a very long paper | This reminds the reader of the meaning of the acronym or initialism. | Reader does not need to flip through pages to recall the meaning |

At the first use of the term in the conclusion. | This reminds the reader of the meaning of the acronym or initialism. | Revises key points of the discussion |

At a later use with a formal definition or proper discussion | This emphasizes the meaning of the full term as part of a focused discussion. | Improves understanding and discussion |

In a table of abbreviations | When required by guidelines, a reader may look up the acronym or initialism in the list. | Serves as a reference for the reader. |

Unfortunately, many journals and style guides specifically request the standard rule of only introducing acronyms and initialisms at the very first use of the full term. Furthermore, some editors with scientific editing companies automatically change to this approach, and journal editors and reviewers may point out late or repeated introductions as errors. It is easy to miss the benefits of reintroducing acronyms and initialisms or introducing them later as part of a formal definition, especially when one is busy and reads very many papers. Therefore, in a later section, I’ll discuss different ways of introducing acronyms and initialisms, and how they can be used to emphasize a repeated or late introduction.