A strong claim means little without support — and using someone else's support without credit can undo an otherwise excellent essay. Here is how to do both properly.
A claim is only an opinion until you show what it rests on. Evidence turns an opinion into an argument, and honest citation tells the reader exactly where that evidence came from.
This guide explains what counts as strong evidence, how to judge a source, the three ways of using a source (quoting, paraphrasing and summarising), how to introduce and explain evidence, how citations work in the main styles, what plagiarism really is (including the accidental kind), and how to use AI tools honestly. It has two worked examples, a checklist, common mistakes, myths and ten practice questions.
It builds on Types of Essays and Thesis Statements, and it connects with Essay Structure, Transitions & Cohesion and Editing Your Own Work. Spelling follows British English.
Strong essays support each claim with credible, specific evidence instead of vague generalisations. "Many people think so" is not evidence. "A named study of named people found this result" is.
| Type | Example | Watch out for |
|---|---|---|
| Facts and statistics | "The experiment lasted nine months." | Say who measured it, and when. |
| Expert opinion | A doctor on health, a historian on history | Is the expert qualified in this topic? |
| Quotation | The exact words of a writer or speaker | Do not use quotations as filler. |
| Example or case study | One school, one town, one company | One case may not prove a general rule. |
| Personal observation | "In my class, most students…" | Fine in a story; weak alone in an argument. |
Notice the third column. Every kind of evidence has a limit, and a good writer says so. That honesty makes an essay more convincing, not less.
Not every page on the internet deserves a place in your essay. Before you use a source, ask four questions:
It also helps to know the difference between two kinds of source. A primary source is the original: a diary, a speech, a set of results, a law. A secondary source explains or discusses the original: a textbook, a news report, a review. Use primary sources when you can, and always say which one you are using. If you read about a study in a news article, it is best to find the study itself and check that the article described it correctly.
Journalists and scientists use the same habit. A news report that names the study, the people studied and the journal lets you check it. A report that says only "scientists say" gives you nothing to check.
There are three ways to use a source. They are often confused, but each has a different job. All three need a citation, because the idea came from someone else even when the words are yours.
Diagram 1. Only a quotation keeps the author's exact words. Paraphrase and summary change the words, but the idea still belongs to the source.
Use the exact words, inside quotation marks, when the wording itself matters: a precise definition, a powerful sentence, or an expert's own claim. Quote sparingly. An essay made mostly of quotations sounds like a collection of other people's sentences, not your argument. Keep quotations short and cut them to the part you need.
Restate one passage in your own words and your own sentence structure, with about the same level of detail. Changing a few words is not enough (see section 9). A good paraphrase shows you understood the passage.
Condense a longer passage, or a whole source, into its main point in your own words. A summary is much shorter than the original and leaves out the detail.
Which should you choose? Quote when the exact wording is the point. Paraphrase when you need the detail but not the wording. Summarise when you only need the big idea. Most of an essay's evidence should be paraphrase and summary, with a few well-chosen quotations.
Evidence should never be dropped into a paragraph without a word of introduction. A quotation with no introduction is called a hanging quote. The reader cannot tell why it is there or who is speaking. Strong paragraphs follow a simple pattern:
Here is the pattern with a real, checked study. It was run by the economist Nicholas Bloom and three co-authors at Ctrip, a Chinese travel company with about 16,000 employees. Call-centre staff who volunteered to work from home were randomly assigned to work from home or in the office for nine months. The authors report that home working led to a 13% performance increase. About 9 points of that came from working more minutes per shift (fewer breaks and sick days), and about 4 points from more calls per minute.
Working from home increases output by 13%. Companies should allow it.
Problems: no source, no setting, and the number sounds like a rule for every job.
Working from home can raise productivity in some jobs. In a nine-month experiment at the Chinese travel company Ctrip, call-centre staff who worked from home performed 13% better than office colleagues (Bloom et al., 2015). The study involved volunteers doing one kind of work, so it does not prove the same gain for every job, but it shows that remote work need not reduce output.
The strong version names the study, says who and what was measured, gives a cautious conclusion and includes a citation. The same study also found that the home workers' promotion rate fell relative to their performance. Mentioning a result like that, when it is relevant, shows the reader you have not chosen only the facts that suit you.
Useful verbs for introducing evidence: reports, argues, found, suggests, claims, notes, shows. Choose the verb that matches how strong the evidence is. A single study "suggests"; a large body of research may "show".
A citation credits the original source of an idea, fact or quotation. It does three jobs at once:
Citations also protect you. A writer who cites carefully can show exactly where each idea came from. A writer who does not may be suspected of copying even when they did not mean to.
Most citation systems have two connected parts. The in-text citation is a short note inside your essay, placed right after the borrowed material. The reference list (or bibliography) is a full list of every source at the end, so a reader could find each one. Each in-text citation must lead to an entry in the list.
Diagram 2. The short note in the text and the full entry in the list work as a pair.
Schools and subjects favour different styles. The common ones differ in small ways, but the purpose is always the same: honest, checkable credit. The table shows one source cited in each style. The last column names the list at the end.
| Style | In the text | Final list |
|---|---|---|
| APA (7th ed.) | (Bloom et al., 2015) | References |
| MLA | (Bloom et al. 165) | Works Cited |
| Chicago notes | A small number¹ with a footnote | Bibliography |
| Chicago author-date | (Bloom et al. 2015, 165) | References |
Here is how the same article would appear in an APA reference list:
Bloom, N., Liang, J., Roberts, J., & Ying, Z. J. (2015). Does working from home work? Evidence from a Chinese experiment. The Quarterly Journal of Economics, 130(1), 165–218. https://doi.org/10.1093/qje/qju032
Points to remember about styles:
Plagiarism is presenting someone else's words, ideas or work as your own, without proper credit. It does not depend on intention. Copying a paragraph on purpose and forgetting a citation by mistake can both be treated as plagiarism, although the penalty may differ.
Plagiarism is about credit, not only about copying words. If you take a clever argument from a website and rewrite it in different words without citing it, you have still used someone else's idea.
What you do not need to cite:
What counts as common knowledge depends on the readers and the subject. A fact that every student in your class knows may be new to someone else. When in doubt, cite. Citing a fact that did not need it is a small fault. Failing to cite a borrowed idea is a serious one.
| Type | What it looks like |
|---|---|
| Direct | Copying exact words with no quotation marks and no citation. |
| Mosaic (patchwork) | Joining phrases from a source, with a few words swapped, and no citation. |
| Self-plagiarism | Handing in your own earlier work again without permission or a note. |
| Accidental | Missing a citation through carelessness or not knowing the rules. |
| Misattribution | Giving the wrong source, or citing a source you never opened. |
| Buying or borrowing work | Submitting an essay written by another person, including a paid service. |
Mosaic plagiarism is the one that surprises honest students. It happens when you keep the original sentence structure and swap in synonyms. The writer thinks "I changed the words", but the sentence is still the source's sentence. You will see an example in section 10.
Self-plagiarism sounds odd, because the work is yours. But a teacher expects new work for a new task. If you want to build on an earlier piece, ask first and say so.
Diagram 3. What decides the answer is credit and honest wording, not how many words were changed.
A true paraphrase is not a copy with new words. Use this method:
Keep careful notes while you research. Mark every copied phrase with quotation marks and the page number in your notes, and write your own thoughts in a different colour or a different section. Most accidental plagiarism begins when notes from a source and notes of your own look the same three days later.
The original sentence below is invented for teaching. It is not from a real source.
Original (Surname, year, p. 12): "Tidal power stations produce electricity predictably, because the moon's pull makes the tides arrive on a timetable that can be worked out years ahead."
Try it yourself. Paraphrase this invented sentence and add a citation: "Regular sleep helps students concentrate in class, because the brain sorts and stores new information during the night."
Sample answer: "Students who sleep regularly find it easier to focus, since the brain organises what it has learned while they rest (Surname, year)." The idea is the same, the sentence is built differently, and the source is credited.
Draft: "Home working led to a 13% performance increase." Schools should copy this.
Improved: A nine-month experiment at the travel company Ctrip found that call-centre staff working from home performed 13% better than office colleagues (Bloom et al., 2015). This shows that home working can succeed in some workplaces. It does not show the same would happen in schools, where pupils need supervision and teachers.
Try it yourself. Write a two-sentence evidence paragraph about a topic you know, using a source you can name. Include a claim, one piece of evidence with a citation and one limit.
AI chatbots can write fluent text in seconds, which makes them tempting and risky for schoolwork. The rules depend on your school, your teacher and your exam board, so always check what is allowed for each task. Some guidance is already clear.
A sensible approach: use AI, if your teacher allows it, to understand a topic or to suggest questions, then find real sources and write the essay yourself. Keep a note of what you asked and what you used. If you are not sure whether a use is allowed, ask before you submit, not after.
Other exam systems have their own rules. Check the regulations for your own board or school and follow them.
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| Mistake | Better habit |
|---|---|
| Dropping in a quotation with no introduction | Introduce it and explain it. |
| Swapping a few words and calling it a paraphrase | Cover the source and rewrite from memory. |
| Citing in the text but leaving the entry out of the list | Check both ends of every citation. |
| Using a statistic with no source or date | Name who measured it and when. |
| Treating one study as proof for everything | Say what the study covers and what it does not. |
| Citing a source you have not opened | Read it, or do not cite it. |
Evidence is what makes an argument worth listening to, and honest citation is what makes it trustworthy. The same habits help you outside school: checking where a claim comes from before you share it, saying where your ideas came from, and being clear about what a study does and does not show. Continue with Transitions & Cohesion to link your evidence smoothly, and Essay Structure to place it in the right paragraph.
Activity: give pupils one short invented passage and ask them to write a quotation, a paraphrase and a summary of it, each with a citation. Swap papers and let partners use the five-step method to test whether each paraphrase is honest. Then discuss what your school allows for AI tools in each kind of task.
Please note: style details (APA, MLA, Chicago, Harvard) vary by edition and institution, and AI rules differ by school, subject and exam board. Follow your own syllabus and teacher. The UK examples describe JCQ guidance and are not a statement about other systems. The study is used as a real example of how to cite; the passages marked "invented" are not from real sources.
12 questions. Select an answer for each, then submit to see your score instantly.