Finally, we should look at how the various rules of grammar and punctuation work around acronyms and initialisms. The rules remain the same, of course, but the nature of acronyms and initialisms means they may be applied in unexpected ways or writers can encounter difficulties in applying them.

Indefinite articles: ‘a’ and ‘an’

First, let’s look at the use of the indefinite article, ‘a’. To revise, this is used before a noun to indicate it is a general, unidentified, or non-specific example of something; e.g., “I picked up a book.” If it is followed by a vowel sound when you read it aloud, then the article used is ‘an’, as in “I picked up an apple.” Here, the ‘n’ sound smooths the gap between the ‘a’ vowel sounds of ‘a’ and ‘apple’ (many languages have little deviations like this for easier enunciation). If ‘a’ is followed by a consonant sound when read aloud, then no ‘n’ is required. However, not all words that start with vowel letters are pronounced as vowels, but instead are said as consonants. For example, ‘ugly’ (uh-glee) and ‘urban’ (ur-ban) both start with vowels but ‘unit’ (yoo-nit) starts with a vowel letter when written but a consonant sound when read aloud. Thus, we have “an ugly vase”, “an urban area”, but “a unit measure”. The choice of whether to use ‘a’ or ‘an’ depends not on the written spelling but on the sound when read aloud.

Let’s see how this rule works when applied to acronyms and initialisms:

  • “…a quantum wave propagator (QWP) approach” and “…a QWP approach”
  • “…an acoustic wave propagator (AWP) approach” and “…an AWP approach”
  • “This is a United Nations project.” and “This is a UN project.”

These work as normal: before the consonant ‘q’ sound of ‘quantum’ and ‘Q’, we use ‘a’, and before the vowel ‘a’ sound of ‘acoustic’ and ‘A’, we use ‘an’. Before the consonant ‘yoo’ sound of ‘United’ and ‘U’, we use ‘a’.
However, consider these examples:

  • “We utilize a liquid crystal display (LCD)…” and “We utilize an LCD…”
  • Does this look wrong on the page? Does it sound wrong if you read it out loud? When we say ‘liquid’, it starts with a ‘l’ sound (a consonant), but when we say the letter ‘L’, we say ‘ell’, which starts with a vowel sound. Therefore, the first case uses ‘a’ and the second case use ‘an’. Let’s look at this again:
  • “In an ultra-high frequency (UHF) band” and “In a UHF band”
  • In this case, ‘ultra’ starts with a vowel sound, ‘ull’, so it takes ‘an’. However, when the initialism is used, the ‘U’ is pronounced as ‘yoo’, so it takes ‘a’. Therefore, we can see that the choice of whether to use ‘a’ or ‘an’ with an acronym or initialism depends on how it is read aloud (or read in your mind’s ear), just like regular words. An acronym that starts with a consonant sound takes ‘a’, while one that starts with a vowel sound takes ‘an’. For an initialism, if the first letter begins with a consonant sound, then ‘a’ is used, but if it begins with a vowel sound, then ‘an’ is used.

Of course, this depends on how a writer and a reader expect to say a given set of initials: one person may see it as an initialism, but another may see it as an acronym. For example, consider these sentences:

  • “The website presents a frequently asked questions (FAQ) page.”
  • “The website presents an FAQ page.”
  • “The website presents a FAQ page.”

The latter two are different, but both are acceptable. In the first case, ‘frequently’ starts with a consonant ‘f’ sound, and takes ‘a’. In the second case, ‘FAQ’ is treated as an initialism, ‘F, A, Q’, where the letter ‘F’ is said as ‘eff’ and takes ‘an’. In the third case, ‘FAQ’ is treated as an acronym pronounced ‘fack’ (similar to ‘fact’), beginning with a consonant and taking ‘a’. You may not know if a particular set of initials is read as an initialism or as an acronym, or if it can be read as both, so it’s often best to just use your own judgment. Consider how you would say the term yourself, how your colleagues would say it in conversation, or look to see how other works in the literature treat the term.

Finally, note that the letter ‘h’ or ‘H’ can be a special case. Some English-speaking areas pronounce the name of the letter as ‘aitch’ and other areas pronounce it is ‘haitch’. The latter case is growing more common, especially among younger speakers, so both are generally acceptable nowadays. Therefore, you can say either ‘an HDD’ or ‘a HDD’, provided you are consistent or follow any journal guidelines, if they cover it. If you’re not certain, look at some local writing or the journal you wish to publish in to see how the letter ‘H’ is treated. You can also ask an English-speaking colleague how they would say the letter. If you’re still not certain, I recommend treating ‘H’ as ‘aitch’—it will look old-fashioned but precise.

Definite articles: ‘the’

The definite article, ‘the’, meanwhile, is used before a noun to indicate that something is a specific case or has been previously identified and is known to the reader or listener. For example, “I picked up a book.” refers to any book, while “I picked up the book.” refers to a specific, previously defined book. Let’s review a previous passage and look at the definite and indefinite articles:

  • “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…”
  • “Pan & Wang developed an 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…”

In the first sentence, an acoustic wave propagator is defined with an indefinite article, and in the second sentence, the same previously defined AWP is referred to with ‘the’. Therefore, unlike the indefinite article, the definite article, ‘the’, works as normally around acronyms and initialisms, provided that they are nouns.

However, if they are not being used as nouns, but instead are adjectives describing something else, then no definite or indefinite article is necessary. Let’s look at this sentence:

  • “The AWP can be expanded using Chebyshev polynomials.”
  • Here, ‘AWP’ is a noun on its own, and takes the definite article. I can alter this to:
  • “The AWP approach can be expanded using Chebyshev polynomials.”
  • This time, ‘approach’ is the noun and ‘AWP’ is an adjective describing which approach this is. Here, ‘the’ applies to ‘approach’, not ‘AWP’. I can rephrase the sentence further to:
  • “AWP expansion can be done using Chebyshev polynomials”
  • In this case, the process of ‘expansion’ is the noun, but as this is neither a specific nor non-specific case, no article is required before it. ‘AWP’ remains as an adjective.

The above are normal grammatical rules, but the situation changes when the initials belong to the name of an organization or establishment, such as a university, research institute, or company. Let’s consider some similar sentences:

  • “She went to work for the National Aeronautics and Space Administration (NASA).”
  • “She went to work for NASA.”

We changed to the acronym, but also abandoned ‘the’. Why was this? In the first case, the full proper name of the organization is ‘National Aeronautics and Space Administration’, which is a proper noun that takes a definite article, ‘the’, as it refers to a specific administration. However, the acronym ‘NASA’ is such a common term that it can be used as a proper name. It no longer refers to a specific administration, so ‘the’ is unnecessary. No one uses ‘the’ unless ‘NASA’ is being used as an adjective for a project or space mission. Let’s try this again:

  • “Shaking table tests were conducted at the National Center for Research on Earthquake Engineering (NCREE).”
  • “Shaking table tests were conducted at the NCREE.”
  • “Shaking table tests were conducted at NCREE.”

In the first case, the name refers to a specific center, so ‘the’ is used. In the second case, ‘the’ can be retained because the initialism is still a specific noun. However, in the third case, ‘the’ can be abandoned, and the initialism be used as a proper name. I’ve found both versions to be common in the literature, and both are grammatically acceptable. Now let’s consider a university:

  • “He studied at the University of Western Australia (UWA).”
  • “He studied at UWA.”

In the first case, ‘the’ is used to refer to a specific university, but in the second case, the initialism is treated as a proper name, so ‘the’ is not required. A definite article is almost never used when referring to a university by an initialism. Finally, let’s consider a certain company:

  • “International Business Machines (IBM) released a new computer…”
  • “IBM released a new computer…”

We don’t have to use ‘the’ at all in these sentences.

You can see that the rules for using the definite article for acronyms and initialisms of names of organizations vary widely. How can we make sense of this? Different style guides give some recommendations. The influential Chicago Manual of Style recommends that if ‘the’ would be used when the name is written out in full, it should also be used for the acronym or initialism. However, this rule is often broken and ‘the’ is neglected when the acronym or initialism is used as a proper name in its own right, which is the case for almost all universities and companies, and many other organizations. I don’t believe there’s a fixed rule for this. Instead, check out the organization’s own documents to see how they present their own name as an acronym or initialism, and whether they use ‘the’ or not.

Plurals

Let’s now look at how to make plurals of acronyms and initialisms.

First, for a plural term, I have seen many writers introduce an acronym or initialism with an ‘s’ at the end. For example, they will write:

  • Common but unclear: “Wave-trapping barriers (WTBs) are a new type of noise barrier.”

Although this maintains the plural form (that is, “WTBs are a new type of noise barrier”), I don’t believe this is necessary. The text in the brackets does not have to follow the grammar of the text outside. In the brackets, we are simply introducing the initial letters of the term ‘wave-trapping barrier’. These are ‘W, T, B’, not ‘W, T, B, s’. That is, ‘s’ is not one of the initials. Later on, we would use the singular form:

  • Correct: “A WTB utilizes a wave-trapping profile on the inside surfaces.”

We can see that ‘WTBs’ is not representative of ‘WTB’. Furthermore, if an acronym or initialism is not clear, a reader might believe that ‘s’ is one of these initials, and that it does not indicate a plural. Therefore, using only the singular case in the brackets reveals the true initialism:

Clear and correct: “Wave-trapping barriers (WTB) are a new type of noise barrier.”

Thereafter, once the acronym or initialism has been introduced, the plural ‘s’ can be added as appropriate. This can be done by simply adding ‘s’ to the end, like so:

  • Clear and correct: “WTBs have already been designed and installed at transformer substations.”

However, there are some older styles and various issues to take note of. One early style was to separate the initials from the ‘s’ with an apostrophe (to indicate a contraction), as in:

  • Unclear: “WTB’s have already been designed and installed at transformer substations.”
    This approach can be very confusing, however, as it looks exactly the possessive form, also using apostrophe-s:
  • Possessive example: “A WTB’s interior surface possesses a wave-trapping profile.”
    This becomes even stranger when we combine the two:
  • Unclear and incorrect: “WTB’s’ interior surfaces possess wave-trapping profiles.”

Therefore, this approach has largely fallen out of use. A few style guides may request it and some writers use it by habit, but it rarely appears in modern academic writing, where precision of meaning is vital. Simply putting an ‘s’ on the end is sufficient.

However, you may wonder how to make a plural if the acronym or initialism already ends in capital ‘S’. In these cases, it is fine to put a lower-case ‘s’ after it:

    Correct: “CMOSs are widely used in modern computing technology.”

The meaning of this should be clear to the reader, especially if the initials have already been formally defined. Some writers add ‘-es’ to the end, in the manner of regular English words ending in ‘s’ (like ‘viruses’ and ‘passes’), such as:

  • Correct: “CMOSes are widely used in modern computing technology.”

Although this is an accepted style, personally I feel this is unnecessary. Adding ‘-es’ to the end of a normal word spells out its pronunciation: e.g., ‘viruses’ (vy-rus-es) not ‘viruss’ (vy-russ) and ‘passes’ (pass-es) not ‘passs’ (pass-ss). When reading out the initials of an initialism, the pronunciation depends on the letters, not the spelling, and ‘-es’ is simply pronounced as ‘s’ (ess) anyway, so this addition is redundant. Nevertheless, it may look clearer and less ambiguous.

However, if the acronym or initialism ends in a lower-case ‘s’ or another lower-case letter, then the plural form will likely be ambiguous:

  • Unclear: “Of the acetolactate synthases (als) occurring in plants, weed alss are homologous to…”

Here, it is not clear if the final ‘s’ means a plural or if it is a letter from the acronym or initialism. Even adding ‘-es’ doesn’t help:

  • Unclear: “Of the acetolactate synthases (als) occurring in plants, weed alses are homologous to…”

These can begin to look like normal words, making the reader wonder if there is a typing error. In these cases, try another approach, such as capitals:

  • Clearer: “Of the acetolactate synthases (ALS) occurring in plants, weed ALSs are homologous to…”

However, if capitals cannot be used for the term, try apostrophes:

  • Clearer: “Of the acetolactate synthases (ALS) occurring in plants, weed als’s are homologous to…”

Or simply rephrase so that the singular form can be used:

  • Very clear: “Of the acetolactate synthases (ALS) occurring in plants, a weed als is homologous to…”

If the original term is plural by default or if it’s an acronym designed to produce an already pluralized word, then no additional pluralization is required. This would be redundant and unpronounceable:

  • Incorrect and unclear: “The Large Magellanic Cloud might be an example of what are known as blue objects observed just undergoing moderate starbursts, or BOOJUMSs (after mythical creatures from a Lewis Carroll poem).”

The case without the ‘s’ is clearest and easiest to read:

Correct and clear: “The Large Magellanic Cloud might be an example of what are known as blue objects observed just undergoing moderate starbursts, or BOOJUMS (after mythical creatures from a Lewis Carroll poem).”

On the other hand, a few initialisms (usually slang and sayings) do include an ‘s’ to indicate the term is always plural. In these cases, a lower-case ‘s’ is required in the introduction of the acronym or initialism:

  • Correct: “Some believe education should focus on reading, writing, and arithmetic (the so-called Three Rs).”

In modern writing, it is conventional to simply put the plural ‘s’ at the end of the acronym or initialism, because it is treated as a whole word in itself. However, an early style was to treat an acronym or initialism as a series of separate abbreviations, with each letter handled separately. So, to make a plural, the ‘s’ was placed after the initial of the word being pluralized, not at the end. For example, in the sentence:

  • Correct: “The members of parliament (MP) gathered at the meeting.”

The word “members” is pluralized. With the initialism and an apostrophe-s plural, this would be written as:

  • Unclear: “The M.’s P. gathered at the meeting.”

This becomes ambiguous when we remove the apostrophe and dots:

  • Unclear: “The M.s P. gathered at the meeting.”
  • Unclear: “The MsP gathered at the meeting.”

Therefore, the modern style places the ‘s’ at the end:

  • Clear and correct: “The MPs gathered at the meeting.”

In some old cases and in a few other languages, pluralization is indicated by duplicating letters of the initialism. This can still be seen in some shorthand notation: ‘page’ is ‘p.’ but ‘pages’ is sometimes ‘pp.’ (though ‘p.’ is also used). ‘Manuscripts’ is sometimes ‘MSS’.

Finally, acronyms and initialisms for terms where a noun is always plural tend not to require an ‘s’ at all. For example, the United States of America is always ‘USA’, never ‘USAs’ or even ‘U. S.’s of A.’ In these cases, the ‘s’ in the original plural noun “States” is combined as part of the initial of the word. That is, ‘S’ stands for ‘States’, not ‘State’.

Other grammar issues

I mentioned above how the apostrophe-s style for plurals of acronyms and initialisms can be mistaken for the possessive form. Let’s briefly look at that the possessive form. In the modern style, this works just the same as for normal words: an apostrophe-s is added to the end of a word, acronym, or initialism to indicate the possessive form:

  • Correct: “A wave-trapping barrier’s interior surface possesses a wave-trapping profile.”
  • Correct: “A WTB’s interior surface possesses a wave-trapping profile.”

The possessive for the plural form works in reverse, with ‘s’ followed by an apostrophe:

  • Correct: “Wave-trapping barriers’ interior surfaces possess wave-trapping profiles.”
  • Correct: “WTBs’ interior surfaces possess wave-trapping profiles.”

If the acronym or initialism ends in ‘S’ or ‘s’, the situation is the same:

Correct: “A CMOS’s floor leakage current ranges from 10−12 to 10−15 A/μm.”

The possessive form is applied the same way when it’s also a plural:

Correct: “The CMOSs’ floor leakage currents range from 10−12 to 10−15 A/μm.”

In academic writing, a sentence generally should not begin with a lower-case letter or a numeral. If a sentence begins with an acronym or initialism that starts with a numeral or lower-case letter, then it is best to rephrase it such that the acronym or initialism does not lie at the beginning, like so:

  • Incorrect: “3D modelling can be performed using…”
  • Correct: “A 3D model can be created using…”
  • Incorrect: “hcp is affected by an SRA.”
  • Clear: “An hcp is affected by an SRA.”

Another way is to simply expand it into the full term:

  • Correct: “Three-dimensional modelling can be performed using…”
  • Correct: “Hardened cement paste is affected by an SRA”

This is another good way to reintroduce the full meaning of an acronym or initialism.

Another chapter in this book will discuss further the use of hyphens and dashes. Here, I’ll briefly cover how these are applied with acronyms and initialisms. First, as acronyms and initialisms are treated as words, they work just the same way, but the results can be confusing or complex. For example, suppose we wish to discuss a technique based on the finite element method (FEM). We can use it in a compound modifier with a hyphen as normally:

Correct and clear: “We demonstrate an FEM-based technique for determining the shear center.”

This is rather straightforward, but what if this is also the first mention of the finite element method and we wish to introduce the initialism as well? The full statement ‘finite element method (FEM)’ is an open compound, so we use the en dash instead of the hyphen:

Correct but unclear: “We demonstrate a finite element method (FEM)–based technique for determining the shear center.”

This appears rather complex, with the brackets followed by an en dash, and multiple statements within the compound modifier. Furthermore, a reader may initially understand this as “We demonstrate a finite element method” rather than “We demonstrate a technique”, so this can be confusing. Although this is technically correct, it may be better to simplify and rephrase:

  • Clear: “We demonstrate a technique based on the finite element method (FEM) for determining the shear center.”
  • Clear: “We demonstrate a technique for determining the shear center based on the finite element method (FEM).”

In these cases, there is no ambiguity and it is simpler for both the writer and the reader.

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