A Guide to Writing a Claim, Evidence, Reasoning (CER) Paragraph for Science

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Learn to formulate a claim, collect evidence, and explain your reasoning

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Coming Up with a Claim

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Collecting Evidence

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Explaining Your Reasoning

When scientists make claims about our world, they justify those claims by citing evidence and explaining their reasoning. “Claim, Evidence, Reasoning,” a.k.a. “CER,” is the backbone of science. Learning how to write a CER paragraph is crucial to thinking like a scientist—not to mention, doing well in science class. This article will teach you how to come up with a claim, collect evidence, and provide your reasoning for a CER. We’ll even provide example sentences to get you started. Keep reading to learn how to draft a CER for your science class.

Things You Should Know

Identify the question you need to answer with a claim, then write a one-sentence answer. This sentence is your claim, which you’ll prove using evidence.
Collect evidence to support your claim such as observations, measurements, and results from experiments. Write 2-3 sentences describing the evidence.
Explain your reasoning by showing how all the pieces of evidence fit together. Then describe how each piece of evidence supports your original claim.

Part 1

Part 1 of 3:

Coming Up with a Claim

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1
Identify a question you need to answer with a claim. A “claim” in a C.E.R. is a statement that answers a question. More specifically, it’s a statement that can be supported with evidence or data. Your teacher or professor may provide you with a question, or you might be asked to come up with your own question to answer with a claim.^{[1]XResearch source}
- For example, your science teacher might provide you with the question “Which has more mass: a cubic meter of water, or a cubic meter of air?”
- Instead of being given the question above, you could be given a table listing the densities of different materials, including water and air.
- You could then use the table to come up with your own question. For instance: “Which material listed on the table has the highest density?” or “What volume of air weighs the same as a cubic meter of water?”
2
Come up with an answer to the question. Choose an answer that you can support with data, common knowledge, or other information you’ve been provided. For example, if the question is “What would happen if water and vegetable oil are stirred together?” your answer could be that the vegetable oil will separate and float on the water.^{[2]XResearch source}
- In this example, you could support your answer by citing data showing that oil is less dense than water, and that low-density liquids float on top of higher-density liquids.
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3
Write your claim by stating your answer in one sentence. Make sure your claim answers the original question. Don’t explain your claim or provide evidence yet.^{[3]XResearch source} Use one of the following formats if you’re feeling stuck:^{[4]XResearch source}
- I will demonstrate that _________________.
  - “I will demonstrate that vegetable oil will separate and float above water if the two liquids are mixed together.”
- Scientists have shown that _____________.
  - “Scientists have shown that a cubic meter of water is more massive than a cubic meter of air.”
- __________ is/are caused by ______________.
  - “The seasons are caused by Earth’s axial tilt.”
- I support the idea that _________.
  - “I support the idea that hydrogen is more chemically reactive than helium.”

Part 2

Part 2 of 3:

Collecting Evidence to Support Your Claim

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1
Gather evidence that proves or supports your claim. Evidence can be observations, measurements, calculations, and information gained from experiments. Choose evidence that’s relevant and doesn’t contradict your claim. To support the claim “Scientists have proven that Jupiter is the most massive planet in the Solar System,” for example, you could gather the following evidence:^{[5]XResearch source}
- A table from an astronomy textbook listing the masses of all planets in the Solar System.
- A scientific article explaining how the planets’ masses were measured.
- The results from gravity experiments taken by a robotic probe that visited Jupiter.
- A separate article that used a different method for measuring the planets’ masses, but came up with the same answers.
2
Select 2-3 pieces of strong evidence. Choose evidence that demonstrates your understanding of the topic. If possible, provide specific data from an experiment you conducted, or from a scientific publication such as an article, research paper, or your science textbook. Note the publication’s name and author so you can cite them later.^{[6]XResearch source}
- If you conducted an experiment, you can use the results of your experiment as evidence to support your claim.
- For example, if you measured the freezing point of salty water vs. fresh water, you could refer to those measurements as evidence for the claim “I will demonstrate that salty water freezes at a lower temperature than fresh water.”
3
Write your evidence in 2-3 sentences, after your claim. Be sure to cite specific authors and articles by name. If you refer to your own experiments, describe the experiments and state the result. Don’t explain why the evidence supports your claim—you’ll do this in the final “Reasons” section.^{[7]XResearch source} If you’re feeling stuck, use the following templates to write your evidence:^{[8]XResearch source}
- __________ states that _____________.
  - “In her article ‘The Mass of Jupiter,’ Dr. Samantha Smith states that Jupiter is more massive than all other planets in the Solar System combined.”
- Our experiment showed _________.
  - “Our experiment showed that salty water freezes at -2°C, while pure water freezes at 0°C.”
- One way to prove ________ is to measure/observe ________.
  - “One way to prove the Earth is round is to observe how objects disappear bottom-first as they approach the horizon.”

Part 3

Part 3 of 3:

Explaining Your Reasoning for Your Claim

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1
Think about why each piece of evidence supports your claim. Make a list of each bit of evidence on a separate piece of paper or document. Then write a few sentences for each bit, explaining why it proves the claim.^{[9]XResearch source}
- “Our experiment showed that salty water freezes at -2°C, while pure water freezes at 0°C.” The only difference between the two types of water was their salt content. This suggests that adding salt caused the freezing point to drop.
- “Seawater near Antarctica is often below -3°C or colder, but doesn’t always freeze.” I know that seawater is salty. This may explain why the seawater doesn’t freeze.
- “Salt is used in cold regions to keep roads from freezing.” Without salt, roads get icy in the wintertime. Salt melts the ice but doesn’t raise its temperature, so the freezing point of salty water must be lower than normal.
- “On pg. 19, the author explains that dissolved salt raises the boiling point and lowers the freezing point of water.” This is consistent with the results of our experiment in class.
2
Draft 1-2 sentences per piece of evidence. Make sure your sentences refer to specific information, measurements, data, or experiments. Use the following templates if needed:^{[10]XResearch source}
- The results of our experiment show ___________.
  - “The results of our experiment show that salty water freezes at a lower temperature.”
- The fact that _______________ proves ______________.
  - “The fact that seawater remains liquid at -3°C proves that salty water has a lower freezing point than pure water.”
3
Use your sentences to write the reasoning section. Begin this section by explaining how all the pieces of evidence fit together. Then use your sentences to explain each piece of evidence, one by one. Use one of the following templates to start your paragraph, if needed:^{[11]XResearch source}
- This evidence supports my claim by ______________.
  - “This evidence supports my claim by demonstrating multiple examples of salty water freezing at a lower temperature than pure water.”
- As you can see from the evidence, _______________.
  - “As you can see from the evidence, Jupiter is clearly the most massive planet in the Solar System.”
- The evidence above proves ______________.
  - “The evidence above proves that hydrogen is more reactive than helium.”