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Guide to Scientific Writing

MERLÍ. Manual d'estil i recursos lingüístics. Criteris lingüístics

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This guide offers you advice on scientific writing.

The purpose of scientific language and writing is to document, report and exchange knowledge in the most direct and objective way possible. Therefore, scientific texts must be:

  • Accurate and precise. Use simple and direct language and avoid vague or ambiguous words and sentences.
  • Clear and concise. Use simple and direct language and avoid unnecessary detail and superfluous words.
  • Objective. Support statements and ideas with appropriate evidence and avoid referring to personal thoughts or beliefs.


[Some of the content of this guide is taken from the Vives University Network’s Interuniversity Style Guide for Writing End-of-Degree Projects in English, an interuniversity project in which the UPC participated with the support of the Government of Catalonia’s Ministry of Research and Universities.]


  • Text layout

    • Structure your text so that the content is easily identifiable: parts of the work, sections and subsections, lists, equations, graphs, diagrams, etc.
    • Apply the right font and size.
    • Use the same font throughout the text.
    • Make sure you align and justify the text.

  • Page numbers and title

    • Add page numbers when you start. The automatic indexing function of your word processor will incorporate these page numbers.
    • We recommend placing the page number at the foot of the page, to the right, and using just one digit, with no dot. Omit the page number on the first page.
    • Include the title of the work in the document header using the automatic function in your word processor. The title is usually left-justified.
    • Use the same font for your title as you have done for the text.

  • Chapters, sections and subsections

    • Number chapters, sections and subsections.
    • Apply the right font and size.
    • Remember that word processors allow you to mark sections and subsections automatically and to use them to create a table of contents or an index.

  • Lists

    • Use numbers, letters, bullets, etc. to list items.
    • To differentiate the items from the rest of the text, indent them slightly.

  • Tables, figures, graphs and equations

    • Place tables, figures, graphs and equations as close as possible to the paragraph in which you refer to them.
    • Centre-justify them.
    • Separate them from the text with a space.
    • Identify them with a number or letter.
    • Remember that word processors allow you to mark tables and figures automatically and to use them to create an index. You can also insert references to these tables and figures in the text.
    • When you are referring to a single figure, use an initial capital letter, e.g. In Figure 1, (…). If you are referring to more than one, use lower case, e.g. In figures 1 and 2, (…)



Paragraphs and sentences


  • Each paragraph must include a topic or subtopic.
  • Avoid single-sentence paragraphs and paragraphs that are longer than five sentences.
  • Structure paragraphs logically: introduction + development + conclusion.
  • Use the appropriate discourse markers to identify paragraphs.
  • Relate paragraphs to one another with the appropriate connectors.
  • Ensure cohesion between discourse markers and connectors.


  • Make sentences short and simple.
  • Keep parenthetical remarks to a minimum.
  • Put important ideas at the beginning.
  • Use the appropriate discourse markers to identify sentences.
  • Relate sentences to one another with the appropriate connectors.
  • Ensure cohesion between discourse markers and connectors.

Discourse markers and connectors

  • Use discourse markers and connectors to identify paragraphs and sentences (with regard to, in relation to, etc.).
  • Use discourse markers and connectors to relate paragraphs and sentences to one another.
  • As far as sequential markers are concerned, do not forget any of the elements and use them appropriately (first, second; firstly, secondly, etc.)
  • Avoid using on the one hand and on the other hand unless you really are contrasting items.



Subjects and verbs

  • Express who is doing the action (the character) in the subject and the action in the verb. Sentences are easy to understand if it is clear who is doing what.

  • Keep the subject short. Readers will understand a sentence more easily if the subject of the verb is short and concrete and if the longer, more complex information comes after the verb.

  • Keep the subject towards the beginning of the sentence. Readers find it much easier to understand long pieces of text if they appear after the subject and the verb than if they do so before.

  • Maintain the subject-verb-object connection. Sentences that keep these elements together tend to be clearer than those that separate them.

  • Respect end focus. End focus is the principle that the new or most important information in a clause or sentence comes at the end.



Vocabulary and terminology


  • Use formal and neutral language.
  • Use the words that are commonly used in a formal register.
  • Use verbs rather than nouns.
  • Use words with a specific meaning and avoid empty nouns and verbs.
  • Use adverbs sparingly.


  • To avoid confusion, ensure terminological consistency, that is, avoid using different terms to refer to the same thing: if you used wave action do not call it wave activity elsewhere in the text.
  • Consult the terminological resources that are available to find terms you were not aware of, to ensure that you are using a term correctly and to check terms in other languages.
  • Provide sufficient information on foreign terms and ensure that the reader knows what acronyms refer to.




Punctuation signs

  • Never put a comma between the subject and the verb.
  • Check the punctuation around parenthetical remarks: make sure there is a comma at the beginning and at the end.
  • Question marks and exclamation marks must be placed at the end of the sentence, with no space. There is no need for additional punctuation.
  • Ellipses: use just three dots, with no space before them, and do not over-use them. An etc. is preferred. Do not use an ellipsis and etc. in combination.
  • Brackets must be closed up to the phrase they are placed around; if they enclose a complete sentence, the punctuation sign must be placed before the closing bracket.
  • Use em dashes to set off parenthetical remarks, but do not over-use them. Em dashes (control + alt + minus sign) must be closed up to the rest of the sentence. If the parenthetical remark comes at the end of the sentence, omit the closing dash.
  • Remember that equations and formulae that are separated from the text but are part of a sentence must be punctuated just as other elements in the text are.



Symbols and acronyms

  • Symbols

    • Use physical, chemical and mathematical symbols in the manner established by international standardisation bodies as far as italics or roman type and capitalisation are concerned.
    • Do not put a dot at the end of a symbol.
    • Leave a space between the symbol and the quantity.
    • Use a non-breaking space (in Word, control + shift + space) between the symbol and the quantity so that they are not separated by a line break.
    • Symbols do not have plural forms.
    • With intervals or ranges, it is best to repeat the symbols for each value.
    • Write the symbols corresponding to names of persons with an initial capital letter.
    • Make sure you use superscript or subscript when necessary.

  • Acronyms

    • Write acronyms in capital letters.
    • Do not use dots in between the letters.
    • If you wish to use the plural, add an -s if the acronym does not stand for a plural already, e.g. ICT, ICTs.
    • Do not italicise acronyms that stand for words in other languages.
    • Use the acronym for the name in the language you are writing in, e.g. OECD, not OCDE.
    • The first time you use an acronym, use the full, written-out form, followed by the acronym in brackets. Use the acronym from then on.



Graphic features of the text

  • Font

    • Do not use more than one typographical resource to highlight an element of the text, e.g. italics + bold + underline.
    • Use italics for words in other languages, Latin terms, words or phrases in a metalinguistic sense, scientific names of animals and plants and titles of books.
    • Use bold for words you wish to draw attention to and for the titles of chapters, sections and subsections.
    • Do not over-use capitals; use them only when necessary.

  • Numbers

    • In any part of your work in which numerical data appear in isolation and surrounded by words, they must be written out if they contain three words or fewer, as long as they are not accompanied by a symbol.
    • Decimals: whole numbers and decimal numbers are separated by a dot (not a comma), with no spaces on either side.
    • Thousands: international standards endorse using a thin or non-breaking space to separate thousands from hundreds. A comma is also acceptable, but remember to be consistent throughout the text.



Equations and formulae

  • Follow the criteria set by international bodies for writing equations and formulae.
  • Use your word processor’s tools for writing equations and formulae.
  • Do not forget to apply the criteria to equations and formulae in the running text.

  • Equations

    • Consider whether an equation would be best presented in the running text or on a separate line.
    • If you set it off from the running text, leave a blank line before and afterwards.
    • Centre-align and indent equations that are part of the solution to a problem.

  • Mathematical formulae

    • Separate mathematical formulae from the text with blank lines before and afterwards, and centre-align them.
    • Leave a blank space between operators and digits.
    • Divide long formulae that are spread over more than one line at the points where any of the following signs appear: + – x =.
    • Do not divide operations in brackets, square brackets, etc.

  • Chemical formulae

    • Incorporate empirical and molecular formulae in the running text; separate semi-structural (condensed) and structural formulae from the running text with a blank line before and afterwards.
    • Do not divide chemical formulae.
    • Only divide chemical reactions using → or +.



Bibliography, in-text citations, references and footnotes

  • Footnotes

    • Footnotes are generally flagged by a superscript number that immediately follows the portion of the text that the note at the bottom of the page refers to.
    • The superscript number is placed after all punctuation marks except the dash.
    • Footnotes should appear on the same page as the portion of text to which they refer.
    • Use the same text size and font, although you can also use the same size as the text of the footnote (in this case, use a dot after the number).
    • Use a smaller size for the footnote than that of the body of the text. Remember that word processors allow you to create footnotes automatically.



How to produce a glossary of terms and write definitions

  • How to produce a glossary

    • Order the terms alphabetically.
    • Write the elements in a term in their natural order.
    • Introduce the full form of the term.
    • Do not include words that are not strictly part of the term.
    • Write the terms in lower case, except acronyms and proper nouns.
    • Verbs: use the infinitive.
    • Write the terms in the singular, except those that only have a plural form.
    • Include terms in other languages in the same list.

  • How to write definitions

    • Include only the specific sense in which you use the term in your text.
    • Express the principal sense in a single sentence. You can add complementary information later if you need to.
    • Use verbs in the present tense in the definition.
    • Start the definition with a capital letter and end it with a full stop.
    • Remember that a definition must not include the definition of another term.



Good writing practices

  • Enable the spell-checker when you start writing. Select the language you are writing in. Be especially careful not to mix British and American varieties of English. 
  • If there are fragments in other languages, select the right language.
  • Remember that spell-checkers have their limitations and may be a source of error.
  • If you copy a fragment from another text make sure there are no mistakes.
  • Eliminate double spaces with the find-and-replace function, as your spell-checker will not detect them.
  • Use the find-and-replace function with care; it can lead to unforeseen changes.
  • When you delete or replace parts of the text, make sure you do not leave behind truncated phrases, inconsistencies, and punctuation and other mistakes.
  • If you use machine translation, revise the result very carefully, as it may be lacking in quality.
  • As you develop the text, reread it, looking out for the different aspects considered in this guide (layers of revision). At the very least, reread it when you finish. It also helps to have someone else read your work and highlight parts of the text in which the writing may be unclear.



Cohesion and coherence

Cohesion refers to the micro-level of the text, the logical connections between words and sentences that give a sense of flow. Coherence refers to the macro-level of the text, the sense that the paragraph or block clearly communicates an idea to the reader. You can use several techniques to ensure that your writing is cohesive and coherent.

  • Exploit repetition. Repetition, particularly of characters in subject position, and constant reference back to previous information give text a sense of unity and focus. 
  • Use transitions, the words and phrases that signal relationships between ideas. See examples of transition words and their functions in the table below.

    Addition Cause/effect Sequence
    In addition
    As a result
    First/In the first place
    Second/In the second place
    Contrast Example Summary
    In contrast
    On the other hand
    For example
    For instance
    By way of example
    In this case
    To conclude
    To sum up
    In conclusion
    In brief
    In the final analysis

  • Move from old information to new. Begin a sentence with familiar information and then go on to add something unfamiliar. This principle goes hand in hand with the principles of characters as subjects and end focus.




Good academic writing is concise. Concise writing expresses its meaning clearly in few words and enables readers to quickly identify key points. It increases the impact of the message because it makes it more memorable. However, although concise texts are easy to understand, they are by no means easy to write because they require considerable revision. It is impossible to identify all the ways in which authors inflate their texts, but below you will find some strategies for reducing length without removing necessary information.

  • Reduce relative clauses to simpler, shorter constructions. 
  • Delete superfluous words and phrases that add nothing to the meaning.
  • Avoid expressing the action of a sentence in the form of a noun (nominalisation).
  • Use constructions that combine it or there with the verb be (expletive constructions) sparingly.
  • Avoid vague attributions (It has been shown that ..., It has been observed that ...). Make a straightforward assertion about generally accepted scientific knowledge rather than a vague attribution.
  • Make direct statements and avoid unnecessary introductions to sentences.
  • Do not hedge to excess. Common hedges include probably, possibly, perhaps, may, might, apparently, suggest and indicate. Although you may sometimes need to use hedges to moderate the forcefulness of your arguments and to show that you are aware of the limits of your findings, using too many weakens the message.



Active or passive

The use of the active or passive voice in scientific writing is the subject of heated debate. Some claim that the passive voice is ideally suited to scientific communication because it gives texts an impersonal tone that is more objective and formal. Others believe that the active is more concise and makes texts more readable and easier to understand.

Should research writers use the active or the passive voice? The answer is, of course, that you should use both. Below are some principles that will help you decide when to use one or the other.

  • Respect your supervisor's or the journal's preferences.

    As a researcher, you will adapt your writing style not only to your individual preferences but also to the external requirements dictated by your field of study and your supervisor. If you are given instructions to favour either the active or the passive, follow them. If you are not, follow the principles below.
  • Use the passive voice to focus on the action.

    In many cases readers do not need to know who or what did the action because the focus is on the object of the action or the action itself. The important thing is not that someone did something but that something was done.

  • Favour the passive voice for methods and results.

    If you favour the active voice for methods and results, you will focus on the researchers. By using the passive you can change the focus to the materials and procedures used or the results obtained, and also avoid a long list of sentences all beginning with I or We.

  • Use the verb form to organise the sentence content.

    As mentioned above, readers find sentences easier to understand if subjects are short and the longer, more complex information is located after the main verb, so your decision on how to express the verb does not depend on your preference for the active or the passive per se but on the position of the verb in the sentence.

  • Use verb forms that keep characters in subject position.

    More important than the decision to express the verb in the active or the passive is the decision about what to place in subject position. Readers understand text more easily if writers locate their main characters in the subjects of their verbs and if these subjects are regularly repeated.

  • Use verb forms that facilitate movement from old information to new.

    As mentioned above, readers expect the information at the beginning of a sentence to provide a familiar context after which new information will be presented, and they feel confused when a sentence begins with information that is new or unexpected.

  • Use the active with the pronouns I or we

    Some claim that first-person pronouns should not be used in research writing because they are not objective, but I and we are used in modern scientific writing in certain ways: to refer to the authors' own writing and thinking, and when the authors are main characters in contrast to other researchers. Thus, they are generally found in the introduction of a research article, where authors state their intentions (I will show that ..., We start by ..., I claim that ..., We argue that ..., etc.), or in the discussion and conclusion, where they compare or contrast their work with the work of others.




Titles have an important function: they immediately reveal to your readers whether you have understood the demands and conventions of your chosen discipline. A good title will attract readers to your text, inform them of the content of your work and show them that you are part of their community.

  • Nominal titles

    Across all genres, nominal titles are possibly the most common title construction. Being the simplest form of title—essentially, a kind of name label—they are efficient and effective. The following is a typical nominal title:

    Determining the Effectiveness of Decontamination with Ionized Hydrogen Peroxide

    This type of title is a sentence fragment, not a full sentence; it is based on noun phrases and contains no finite verbs. It is 'indicative' in that it merely indicates what the paper discusses but gives no information about the findings. Good nominal titles are effective because they are specific but also reasonably short. You need to be able to strike a balance between including as much detail as possible while still keeping your title short.
  • Compound titles

    A compound title offers context and then specific details. For example:

    Cognition and Alertness in Medical Students: Effects of a Single Night of Partial Sleep Deprivation

    The title is still nominal but, unlike the other title above, it is also compound: it consists of two sentence fragments based on noun phrases joined by a colon. It specifies the nature of the study but remains compact. The first phrase gives a general description of the subject, which the second phrase explains in more detail.

  • Full-sentence titles

    Studies in some branches of science result in conclusive, evidence-based results. When this is the case, authors may assert their findings in a full-sentence title:

    Memantine treatment reduces the incidence of flaccid paralysis in a zika virus mouse model of temporary paralysis with similarities to Guillain-Barré syndrome

    Note that the verb is in the present tense and that this underlines the applicability of the result to other cases.

    Bear in mind that your title is the single most important phrase in your study, so make sure you give it the time and effort it deserves.

    • Decide which word is the most important and, if possible, place it prominently in initial position.

    • Write a working title early in the research process to focus your efforts; by constantly referring back to it, you can keep your research and your writing on track.

    • Revise and modify it during the research process and only submit a final version once the research is complete.

    • Unless you are instructed otherwise, capitalise the first word of the title and all its nouns, pronouns, adjectives, verbs and adverbs; do not capitalise any articles, conjunctions or prepositions. 

    • Write terms out in full and avoid using abbreviations, unless the abbreviation is more readily understandable to readers in your field that the written-out form.

    • Do not finish a title with a full stop.



Abstract and keywords

  • Abstract

    The purpose of an abstract is to quickly and clearly provide an overview of your work, so:

    • Begin with and focus on the most important information.

    • Lead with the hypothesis, question or problem that you have been researching.

    • Do not give details that are not of primary importance and that should be explained elsewhere in the text, not the abstract.

    • Do not define technical terms or explain concepts here. 

    • Write it as a single paragraph. (Abstracts are typically between 200 and 300 words long.)

    • Structure your abstract as follows: background, aim(s), method, results and conclusion.

    • Use verbs in the present tense, reflecting the current significance of your areas of study.

  • Keywords

    Keywords play a fundamental role in ensuring that other researchers can find your work. To decide which words and phrases to include in this section:

    • Think about the main topics of your research and which terms you would type into a search box to find it.

    • Include the following: words related to the main field of study, the most frequently used terms in your document, synonyms for some of the main concepts, acronyms and any other term you feel may optimise a keyword search.



Oral presentation

  • Consult Class Talk for advice on improving your oral presentation in the classroom in English.