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Claims, evidence and reasoning are the basic parts of writing a scientific explanation. When writing about a science topic, authors may be faced with a challenging question or problem that they must address. The claim answers the question or addresses the problem. The author must support the claim with evidence that is sufficient and relevant to the claim. The author must also include reasoning that adequately explains how the evidence supports the claim. A well-written explanation helps the reader better understand the topic.

Read the following excerpt from the Newsela article ”California tries one solution to water problems – treating seawater,”opens in new window and then watch the slideshow below to learn how to develop an explanation with claims, evidence and reasoning.


California tries one solution to water problems – treating seawater

1 Along this patch of the Pacific Ocean, construction crews nearly outnumber the surfers and sunbathers. Workers are busy assembling what some hope will make water scarcity a thing of the past.

2 They are building the Carlsbad Desalination Project. When it is completed, the huge plant will turn as many as 56 million gallons of seawater each day into drinking water for San Diego County. The project is expected to cost $1 billion.

3 The desalination plant is being built by Poseidon Water, a private company. Customers in the city of San Diego will help pay for the plant through their water bills, which could go up by $5 a month.

4 The building will house more than 16,000 reverse-osmosis membranes — salt filters, essentially. They will turn Pacific Ocean water into drinking water suitable for making coffee and watering lawns.

– Newselaopens in new window, December 4, 2014


Now, explore the following slideshow to learn how claims, evidence and reasoning are used in developing a written explanation. Keep in mind the excerpt that you read and make note of portions of the slideshow that confirm or contradict your own ideas related to the claims, evidence and reasoning in this portion of the article.


Speaker plays audio

Claims, Evidence and Reasoning

close up of hands on laptop; graphic displaying written explanation with claim, evidence and reasoning bullet points.

A written explanation needs to be easy for your reader to understand. Claims, evidence and reasoning will help the reader better comprehend the topic that you are explaining.

A claim is a statement that answers a question or solves a problem. It is the main point that the author is making.

Flowchart claim at top - Claim: Even though desalination is very expensive, it may solve California’s water problem; arrow pointing to evidence – Evidence: Evidence: Facts. Data. Examples, Research Findings, Quotes from Experts

In this section of the article, the claim can be determined by reading all four paragraphs and thinking about the problem the author is presenting. Careful reading reveals that the problem is the lack of water in California. The solution is desalination, but it is very expensive. In order to capture the claim, think about how to put these ideas together in a statement.

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To support the claim, the author must provide evidence.

Evidence can be presented with facts, data, examples, research findings and quotes from experts. Make sure to include sufficient evidence to prove your claim.

Flowchart claim at top - Claim: Even though desalination is very expensive, it may solve California’s water problem; arrow pointing to evidence – Evidence: The project is expected to cost $1 billion.(Data proving expense) Customers in the city of San Diego will help pay for the plant through their water bills, which could go up by $5 a month. (Data proving expense)They will turn Pacific Ocean water into drinking water suitable for making coffee and watering lawns. (Example illustrating the solution to the problem)

Look at the evidence that the author used to support this claim.

Flowchart: Claim at top; three arrows pointing to three boxes with the words evidence in each; evidence boxes poining to reasoning box

An author must also include reasoning to explain how the evidence supports the claim. Logical and valid reasoning will help the reader understand and accept the claim.

Flowchart claim at top - Claim: Even though desalination is very expensive, it may solve California’s water problem; three arrows pointing to evidence; evidence pointing to reasoning; reasoning box: Some hope water scarcity will be a thing of the past because of the efforts to build the desalination plant.

Look at the reasoning that connects the evidence to the claim. Notice that this author does a great job blending these elements of writing. The reasoning is near the beginning of the section. Good writers integrate the claim, evidence and reasoning within sections and throughout the article.

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Knowing how to be an analytical reader will help you apply the skills of explanation to your own writing. As you read explanatory writing, make note of the claim, evidence and reasoning that the author uses.