Previous research is invaluable to scientists–it prevents us from having to “reinvent the wheel” and allows us to continually build upon one another’s progress. It also provides context, support, and explanations for new research findings and interpretations. Therefore, one goal of citing sources in your writing is to point readers to information you have used as the basis of your research so that they can:

  • evaluate the significance of your research questions,
  • examine the validity of your methods and conclusions,
  • and find more information on your topic(s).

Knowing how to use and cite the literature correctly is a critical skill for all scientific writers. In this section, you will learn to

  • Avoid plagiarism
  • Find previously published research that is relevant to your topic
  • Paraphrase others’ information and ideas
  • Decide what should and should not be cited, including whether or not something is common knowledge.


In addition to these fundamental concepts, which are critical to being a thorough, professional, and honorable author, we have also included information on how to format citations and references in separate sub-sections of this page.


How can I avoid plagiarizing?


Your credibility as a scientist is at risk if you are ever thought to have plagiarized even a small part of a paper. Many people don’t intend to plagiarize, but accidentally do so because of poor note-taking or citation practices. Thus, it is paramount that you are familiar with what is and is not plagiarism before starting to write your own work.

Some practices are clearly plagiarism, such as buying someone’s paper online and calling it your own, copying a paper that someone else wrote, or hiring someone to write a paper for you.

But what else constitutes plagiarism?  In general, the wording, ideas, works cited, and/or organization of your paper or individual sections should not map directly on to those of anyone else’s paper, regardless of whether or not their paper has been published. Fundamentally, each of these aspects of writing must be your own. If you find yourself relying heavily on a small number of sources for what to say, how to say it, in what order to present it, you’re in a creative grey zone and should expand the number of resources you’re taking advantage of. If you’re ever in doubt, just ask your professor!


Strategies for avoiding accidental plagiarism
  • Check with your professor about their expectations for group work before starting an assignment. How much of it you can discuss with your peers will vary depending on the class, professor, and assignment, so it’s a good idea to fully understand what you’re allowed to do before accidentally crossing any boundaries.
  • Keep a careful log of the resources you use when researching a topic. If you forget to write down where information came from, it can be difficult to find it again, which could cause you to not cite it at all. Research tools, including reference management software like Zotero, can make saving citation information for a project much easier.
  • Cite paraphrased information and know how to paraphrase well (see below).
  • Before peer-reviewing a classmate’s or labmate’s paper, be sure that you already have your own ideas written down, so that you don’t misremember their ideas as your own.


How do I find useful sources?


Using databases with keyword searching


Numerous online databases are available, which collectively contain hundreds of thousands of peer-reviewed journal articles. Some that give Middlebury students easy access to thousands of journals include:

  • Scopus (, an abstract and citation database of peer-reviewed literature and quality web sources with tools to track, analyze and visualize research. Its content falls most heavily in the physical and life sciences, but it also covers social sciences and humanities literature.
  • ScienceDirect (, a database of medical and life-science articles and books
  • PubMed Central (, a free full-text archive of biomedical and life sciences journal literature at the U.S. National Institutes of Health’s National Library of Medicine (NIH/NLM)


There are many great strategies for finding the articles most useful to you. If you’re a member of the Middlebury community, connect with Wendy Shook, the college’s Science Data Librarian, for some great guidance on how to navigate these databases most effectively.


Footnote chasing and cited reference searching

If you’ve found an article that is highly relevant to your topic, you can use it to help you find more good resources:

  • by looking at papers it references (called “footnote chasing”). This is a way of looking back in time to see what research helped form the basis of the paper you are already using.
  • by looking at papers that reference the paper you’re looking at (called “cited reference searching”). This is a way of looking forward in time to see how the paper you have contributed to more recent work.

You can implement both these strategies by using an publication database, as above. Many such sites contain tools such that when you click on a particular article, hyperlinked lists for “References” and “Cited by” will immediately appear, allowing you to follow numerous links to further sources.



When should I reference a source?


The number of citations you use isn’t what’s important. Use as many sources and citations as are necessary for giving credit for your ideas and backing them up—and no more. That said, the number of works you cite in your writing does vary by genre and upon the intended audience and purpose of the piece. For example, 

  • Posters only cite the most essential pieces of information; they often utilize fewer than 5 citations because they share mostly original work and not much background information.
  • Journal articles, too, only cite literature essential to providing sufficient context for the research and support for the conclusions, but because they are longer and more in-depth, the number of citations is typically on the order of tens.
  • Research proposals usually involve the largest number of citations (around 50-100) because an in-depth literature review is a major component of the document.


A paper should be referenced for its original results only, which include new data or findings reported in a research article results section; new analysis of results integrated from many other papers, such as might be presented in a metastudy results section; conclusions about the state of the field, such as in a review article; among other types of information. The key is that you should reference a paper for its authors’ ideas and findings, and not for what those authors reported that yet other authors reported. For example, you would not reference a paper for information presented in its introduction section about what previous papers had reported. You should always reference the original source of the information and ideas.

So, before referencing a piece of information, ask yourself:

Is this an original contribution by this author?

If not, you may need to trace the data back to the original contributor.


For example, if the introduction of Article A states:

“Gold nanoparticles have unique optical properties such as distinctive extinction bands in the visible region, due to surface plasmon oscillation of free electrons[Article B],”

Article A should not be referenced to support data you collected that shows distinctive extinction bands of gold nanoparticles. Instead, find the original source of the information — Article B — in order to verify the validity and context of those data. If it all checks out, reference Article B as support for your data. 


Tips for determining the necessity of a citation 
Do cite Don’t cite
Primary literature

  • Peer-reviewed journal articles
    • Methodologies
    • Instrumentation
    • Results
  • Technical reports
  • Patents and regulatory/government documents
General knowledge works

  • Lab handouts
  • Undergraduate textbooks
  • Encyclopedias, including Wikipedia*


*Don’t stop at Wikipedia! The reason that you shouldn’t cite general knowledge works is that they are typically only used to prepare the writer for engaging with the primary literature. General knowledge works generally do not include the sophistication and nuance necessary to prepare you to achieve your writing goals, nor are their methods of peer-review, if any, sufficiently known and reliable. If you need help understanding the terminology of a paper, Wikipedia is a great place to start. But peer-reviewed scientific and other validated technical resources are the only types of sources that are reliable and nuanced enough to properly contexutalize your research and support your results and conclusions.


Lit-1: Test yourself

If you got information from one of the following sources, what is the best way for it to be cited? Choose either A, B, C, or D:
A) Information should be paraphrased and cited.
B) Information should be paraphrased, if used at all, but typically not cited.
C) Information should be tracked to its original source before determining A or B.

  1. The abstract of a primary research article published in Nature
  2. Data from a review article published in Physical Review C
  3. A graph from the Results section of a research article published in Analytical Chemistry
  4. An article on Wikipedia
  5. A chapter from your textbook Introduction to Mineralogy
  6. Your Biology 145 lab manual
  7. Information from a data table in a metastudy published in Science
  8. The Vermont Agency of Agriculture Regulations for Control of Pesticides


  1. C – The information should be found in the body of the text before citing so that you fully understand the context of the data. Learn more about abstracts here.
  2. A or C – The answer here depends on the nature of the data. If the data originated in their entirety in another paper, choose C; if the data you are looking to reference from the review paper represent an original compilation, comparison, or other type of integration or reanalysis of others’ data, then you can reference the review article itself.
  3. A – Graphs are often a great summary of information that can be referenced in your paper.
  4. C – Some of the information may be from primary sources, which you can locate using footnote chasing and then cite the original work. Some of the information on Wikipedia may not be properly referenced, so you will need to search for appropriate citable sources on your own. Yet other information on Wikipedia will represent general knowledge, such that it does not need to be cited.
  5. B – Undergraduate or other introductory level textbooks are considered general knowledge work and are not typically referenced. Graduate or advanced level textbooks may be referenced.
  6. B – This is not a primary source and thus should not be cited in professional documents. If you would like to use information from the lab handout, you would need to determine whether it is considered general knowledge (not cited) and if not, find sources containing the original information. Note: Some classes may require the citation of their manuals for work submitted in that class. Be sure to check with your professor for his or her expectations!
  7. A – Metastudies are great resources for finding information from lots of research compiled in one place. Because the analysis of all the data is usually new and different than in the original research, metastudies are considered to contribute something original to the scientific literature and are, therefore, primary resources.
  8. A – Regulatory documents and permits are considered primary sources and should be cited.




Is it common knowledge?


Sometimes, it can be hard to determine whether the information you are using is common knowledge or if you actually learned the information somewhere recently from a source that would need to be cited. Indeed, what is considered common knowledge changes over time, making it a moving target.


Before neglecting to cite something because you think it might be common knowledge, ask yourself:


  • Could I find it in an undergraduate or introductory textbook specific to this discipline? If so, you probably don’t need to cite it.
  • Has it been well established as a scientific fact? Some theories and findings have been backed up by so much evidence for so long that new evidence is unlikely to alter them significantly, if at all. If it is now considered an established fact (e.g., that the Earth orbits the Sun; that global warming is occurring), you probably don’t need to cite it.
  • Can the information be credited to one person or group of people? If so, you probably do need to cite it, unless it has also been accepted as a scientific fact. For example, even though the discovery of the double-helical structure of DNA can be accredited to Watson and Crick’s ideas based on Franklin’s data, this fact has been so widely accepted that it can be found in any molecular biology textbook and does not need to be cited anymore. Some of the more specific properties of DNA are less well-known or less well established, and would probably have to be cited.


A good rule of thumb from the OWL at Purdue is that you can be confident that something is common knowledge if you can find the same information un-cited in at least five credible sources. This sounds pretty tedious, but it is a great way to ensure that you’re not crossing any fine lines.

Whether or not something is “common” knowledge is also largely dependent on your audience, which means that a piece of information cited in one document may not need to be cited in another. Something might be obvious to a more experienced or expert reader of your research proposal, but be entirely new to someone looking at your poster at a symposium.

Because there are no hard-and-fast rules for determining whether or not something is common knowledge, the best option remains: when in doubt, cite it.



When and how should I paraphrase?


In science, unlike in many other disciplines, direct quotations are rarely used. What is important to scientists is the information, not who said it or the exact words they used, so information is paraphrased (and still cited) whenever possible.


For example, if an article you’ve found states: “The activity of hexokinase was found to be reduced ten-fold in the presence of equimolar concentrations of allose,”

  • Do not write in your paper: “Hexokinase activity has been found to be ‘reduced ten-fold in the presence of equimolar concentrations of allose'[citation]”
  • Instead, paraphrase, such as: “Hexokinase is inhibited by allose[citation]”


Strategies for paraphrasing
  • Pick out only the most important piece(s) of information from the passage and make note of them.
  • When you take notes, avoid copying the text verbatim. Using yto our own words in your notes will help you paraphrase the ideas when you write your own paper.
  • Be sure that you’re not only changing the (non-critical) words the original author used but also the sentence structure. Minor alterations to another’s statement, even with a citation, is still plagiarism.
  • Cite it. Even when it’s paraphrased, the idea/information is not your own.


An example of good and bad paraphrasing (adapted from “What is Good Writing?” 2015):

Original passage

Writing is a process. When producing a piece of writing for an audience, experienced writers use systems they have developed. Each writer has an idiosyncratic combination of thinking, planning, drafting, and revising that, for him, means “writing” something. No matter how an individual describes his process (e.g., “First I think about my idea then dump thoughts onto the computer,” or “I make an outline then work out topic sentences”), each person (usually unconsciously) negotiates the series of choices required in his individual context and produces a draft that begins to capture a representation of his ideas. For most people, this negotiation includes trial and error (this word or that?), false starts (beginning with an example that later proves misleading), contradictions (I can’t say X because it may throw Y into question), sorting (how much do I need to say about this?), doubt about how the idea will be received, and satisfaction when they think they have cleared these hurdles successfully. For most people, this process happens through language. In other words, we use words to discover what, how, and why we believe.

Plagiarized version

Writing is a process. When writing for a certain audience, mature writers utilize tools they have cultivated. The thinking, planning, drafting, and revising that happens for each writer is unique. Whichever way someone describes these processes (such as, “I first just dump my ideas onto paper,” or “I make a careful outline and work from that”), everyone makes these choices based upon his or her context and produces a draft that starts to represent their individual ideas. For most people, this involves a lot of trial and error (which word do I choose?), bad starts (starting to give an example that you realize doesn’t work later), sorting (how much should I say about this topic?), contradictions, and satisfaction once these difficulties have been overcome. Much of these decisions come through language–when our words show us what we believe and why.

Appropriately paraphrased version

Over time, authors tend to develop their own techniques and strategies for writing. Each stage of the writing process is accomplished differently depending on who we are. Regardless of what this process looks like or means to a particular writer, all of us make numerous choices throughout their writing including decisions about word choice, level of detail, and organization. Often, through grappling with and eventually making these choices, the language we use and the process we took to find that language helps us better understand our own beliefs.


An example of paraphrasing from a geology paper

Original passage:

The Himalayan–Tibetan orogen, formed by the collision of India with Asia, is the most outstanding natural laboratory for studying the complex geologic processes through which collisional orogenesis evolves. Before the collision, northward subduction of the Neotethyan oceanic lithosphere under South Asia gave rise to an Chilean/Andean type convergent margin. Extensive igneous rocks thus produced in southern Tibet are now exposed as the Gangdese batholith in the Lhasa terrane (adapted from Lee et al. 2009).

Plagiarized version:

When India and Asia first collided, the Himalayan-Tibetan orogen was formed. This structure now serves as one of the most important landmarks for studying the complicated geologic processes behind the evolution of collisional orogenesis. Prior to the collision, the subduction of the Neotethyn oceanic lithosphere northward under South Asia led to an Andean-type convergent margin. This produced an expanse of igneous rock in southern Tibet that are now understood as part of the Lhasa terrane.

Appropriately paraphrased version:

The subduction of the oceanic lithosphere of Northern Neotethyn under South Asia was the beginning of the eventual convergence of India with Asia. The resulting formation of the Himilayan-Tibetan orogen serves as a critical structure of study for understanding the evolution of such major collisional events.


An example of paraphrasing from a chemistry paper

Original passage

Metallic nanomaterials are attractive for sensing, imaging, transport, and cancer therapy applications because of their unique surface plasmon resonance (SPR) enhanced light scattering and absorption. The SPR and SPR-related properties of nanomaterials can be tailored through the adjustment of metal nanoparticle size, shape, and chemistry. Furthermore, the surface chemistry of metal nanoparticles (e.g., gold) enables the facile functionalization of these materials with a variety of ligands. Such nanoparticle-conjugated species may include therapeutic DNA or drug molecules, selective targeting agents, such as antibodies or peptides, as well as a variety of other proteins, molecules, and synthetic polymers (adapted from Dickerson, Sandhage, and Naik 2008).

Plagiarized version

Because of their surface plasmon resonance (SPR) which enhances light scattering and adsorption, metallic nanomaterials are promising for applications in sensing, imaging, transport, and cancer therapy. Through changes to nanoparticle size, shape, and chemistry, the SPR properties of the particles can be adjusted to suit various needs. The surface chemistry of gold and other metal nanoparticles allows for functionalization with a variety of ligands, allowing for such species as drug molecules, selective targeting agents, and other proteins, molecules, and synthetic polymers.

Appropriately paraphrased version

Surface plasmon resonance (SPR) enhances the light scattering and absorption of metallic nanomaterials, making them promising molecules for a variety of biological applications. Changes in the size, shape, and/or chemistry of these nanomaterials results in changes in their SPR qualities, including increased functionality with numerous ligands important for drug design and polymer synthesis.


An example of paraphrasing from a physics paper

Original passage

The probability of tunnel ionization decreases exponentially with decreasing field strength. Consequently, atoms driven by a few-cycle wave eject only a few electron wave packets with significantly differing energy distributions due to significant differences between the field amplitudes in the subsequent half cycles of the pulse. This has two major implications: the emission of the most energetic electrons (i) can be confined to a single wave cycle at the peak of the pulse, and (ii) its temporal profile is most sensitive to the CE phase of the pulse. This opens the door to controlling electron dynamics in the sub-fs domain (lightwave electronics) and—by allowing measurement of the CE phase—control of light waveforms (lightwave engineering) (adapted from Krausz and Ivanov 2009).

Plagiarized version

The likelihood that an electron will undergo tunnel ionization decreases exponentially as the strength of the electric field decreases. Thus, only a few electron wave packets with greatly different energy distributions are ejected by atoms driven by a few-cycle wave because of differences in the resulting half-cycle pulse field amplitudes. The major implications of this for the most energetic electrons emitted are that 1) they can be restricted to a peak single wave cycle and 2) their temporal behavior is affected most greatly by the CE phase of the pulse. These qualities present opportunities for controlling both electron dynamics in ranges below the femtosecond and light waveforms, known as lightwave electronics and engineering, respectively.

Appropriately paraphrased version

Opportunities for light-wave engineering have been presented through evidence that electrons can be controlled in temporal dynamics below the femtosecond. Because atoms that are driven by a small field strength eject minimal electron wave packets with energy distributions that significantly differ from each other, the most energetic electrons emitted can be restricted to a single wave cycle and is most sensitive to the CE phase of this pulse.


An example of paraphrasing from a biology paper

Original passage

The ER is the key compartment in the cell to facilitate folding of newly synthesized proteins and initiate the pathway of vesicular movement of membrane and proteins to various organelles and the cell surface. In mammalian cells, the ER also serves as the major intracellular Ca2+ reservoir. A number of ER stress stimuli, for example, expression of aggregate-prone proteins, glucose deprivation (resulting in reduced glycosylation and decreased energy for chaperone activity), hypoxia and oxidative stress (causing decreased disulfide bond formation), and Ca2+ efflux from the ER, lead to the accumulation of unfolded proteins in the ER, which exceeds its folding capacity. An increasing number of studies indicate that autophagy is induced by ER stress in organisms from yeast to mammals. However, the signaling mechanisms linking ER stress to autophagy vary, dependent on the specific stress conditions and the organisms being studied (adapted from He and Klionsky 2009).

Plagiarized version

A key component of the cell is the ER, which takes part in the folding of newly synthesized proteins and initiates the trafficking of membrane and proteins to organelles and to the surface of the cell. In addition, the ER is the primary reservoir for Ca2+ among cells. Unfolded proteins will accumulate in the ER as a result of various stressors including aggregate-prone protein expression, glucose deprivation, hypoxia and oxidative stress, and Ca2+ outflow from the ER, which can lead to autophagy in numerous organisms. The signaling mechanisms that link ER stress to autophagy vary, however, depending on the conditions of the stress and the study.

Appropriately paraphrased version

Although the ER critically folds newly synthesized proteins in the cell, stressors such as oxidative stress and low glucose levels can cause its over-accumulation of unfolded proteins. ER stress can in turn cause autophagy through a variety of signaling mechanisms.


Note how in the above examples, paraphrasing consolidated the information into fewer words! This is a major advantage of paraphrasing over using direct quotations.


Lit-2: Practice exercise


Paraphrase each of the following by changing both the wording and structure of the passage while retaining the important scientific information.

  1. HCN emission, which is very strong in most ultraluminous galaxies, originates in the high-density extreme starburst regions similar to A and B. These regions do not produce most of the CO luminosity, but they do emit most of the HCN luminosity (adapted from Downes and Solomon 1998).
  2. The dynamic nature of drinking water treatment processes exerts a strong influence on removal of pathogens from raw waters. Pathogen removal efficiency in a conventional treatment plant is affected even with a slight variation in influent water quality or influent water conditions (adapted from Upadhyayula et al. 2009).
  3. Dendrimers are highly branched macromolecules having precisely defined molecular structures with nanoscale size. Complexes containing dendritic ligands are also soluble in many common solvents and can be separated from the products by precipitation, membrane or nanofiltration techniques (adapted from Fan, Li, and Chan 2002).

Possible solutions

All solutions should attempt to both alter the organization of the original passage and be in your own words. Remember that the original source will still need to be cited.

  1. High-density starburst regions such as A and B are responsible for most of the HCN luminosity (but not CO luminosity), as in most ultraluminous galaxies.13
  2. Minor variations in the quality of influent water can significantly affect the processes required for efficient pathogen removal in drinking water treatment plants.4
  3. Precipitation, membrane and nanofiltration are all techniques capable of separating dendritic ligand complexes from the products.7

Some of these example solutions may seem to cut out important information. The key is to know what information is critical for you to use and to cut out anything else.




How do I format citations and references?


There is no universal rule for formatting citations in your paper and constructing the reference section at the end. Most important is that you keep your style consistent throughout your paper.

More information on formatting citations is available here (The Essentials > How do I find and use the literature? > Formatting citations).

More information on formatting references is available here (The Essentials > How do I find and use the literature? > Formatting references).