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Types Of Evidence In Critical Thinking

Critical thinking means being able to make good arguments. Arguments are claims backed by reasons that are supported by evidence. Argumentation is a social process of two or more people making arguments, responding to one another--not simply restating the same claims and reasons--and modifying or defending their positions accordingly.

Claims are statements about what is true or good or about what should be done or believed. Claims are potentially arguable. "A liberal arts education prepares students best" is a claim, while "I didn't like the book" is not. The rest of the world can't really dispute whether I liked the book or not, but they can argue about the benefits of liberal arts. "I thought the movie was cool" is not an arguable statement, but "the movie was Paul Newman's best" is, for people can disagree and offer support for their different opinions.

Reasons are statements of support for claims, making those claims something more than mere assertions. Reasons are statements in an argument that pass two tests:

Reasons are answers to the hypothetical challenge to your claim:

  • “Why do you say that?”
  • “What reason can you give me to believe that?” If a claim about liberal arts education is so challenged, a response with a reason could be: “It teaches students to think independently.”

Reasons can be linked to claims with the word because:

  • Liberal arts is best [claim] because it teaches students independent thinking [reason];
  • That was Newman's best [claim] because it presented the most difficult role [reason];
  • Global warming is real [claim] because the most reputable science points in that direction [reason].
  • Everyone should stop wearing seat belts [claim] because it would save lives [reason].

If reasons do not make sense in the hypothetical challenge or the 'because' tests, there is probably something wrong with the logic of the argument. Passing those tests, however, does not insure that arguments are sound and compelling.

Evidence serves as support for the reasons offered and helps compel audiences to accept claims. Evidence comes in different sorts, and it tends to vary from one academic field or subject of argument to another. Scientific arguments about global warming require different kinds of evidence than mealtime arguments about Paul Newman's movies. Evidence answers challenges to the reasons given, and it comes in four main types:

Specific instances include examples, case studies, and narratives. Each can be an effective mode of building support for a reason or claim. In a public speech, they offer audiences a way to see an idea illustrated in a particular case. To be effective, specific instances need to be representative of the broader trend or idea they are supporting. With an example as evidence, someone arguing against seat belt use might say "Last year my cousin crashed her car off a bridge and would have drowned if she were wearing her seatbelt" as evidence (the answer to "Why do you believe that?" question.) An opponent might challenge whether this example was a representative one: surely there are many more car crashes that do not end in water, so this one instance is not a fair gauge of the relative safety of not wearing seat belts.

Statistics include raw numbers (117 million visitors to the Rock and Roll Hall of Fame,), averages ('women's bowling teams drink on average two pitchers less then men's'), statistical probabilities ('crossing North Main during rush hour increases your chances of death 20%'), and statistical trends ('applications have risen 40% over the past three years'). In public speeches, statistics have the advantage of seeming objective, authoritative, and factual, but critical audiences will want to know about the sources and methods for determining your statistical evidence.

Testimony, or appeals to authority, come in two main types, eyewitness and expert. Eyewitness or first-hand testimonies are reports from people who directly experience some phenomenon. If a speaker is arguing about toxic waste dumps, a quotation from someone living next to a dump would fall into this category. First-hand testimony can help give the audience a sense of being there. Experts may also rely on direct experience, but their testimony is also backed by more formal knowledge, methods, and training. Supplementing the neighbor's account with testimony from an environmental scientist, who specializes in toxic waste sites, is an appeal to expertise. When using testimony in arguments, you should always make sure the authority you are appealing to is in fact qualified to speak on the topic being discussed.

Using critical and analytical thinking may seem daunting at first, but by following a series of clearly defined steps, you can start to use such skills sooner than you may have imagined.

What is critical and analytical thinking?

Critical analytical thinking is a key part of university study. Many first year students receive comments such as 'not analytical enough' on their early assignments. You will find that you develop your critical and analytical skills as you go through university. In brief, this means looking very closely at the detail and not taking what you read or hear for granted. Your tutors will expect you to:

  • Evaluate how far materials are appropriate, and up-to-date.
  • Evaluate how far the evidence or examples used in materials really proves the point that the author claims.
  • To weigh up opinions, arguments or solutions against appropriate criteria.
  • To think a line of reasoning through to its logical conclusion.
  • Check for hidden bias or hidden assumptions.
  • Check whether the evidence and argument really support the conclusions.

You will need to do this for materials that you read. For example, when you cite a source of evidence for your own arguments, you will need to be sure that the evidence really does support your point, and is accurate and reliable. You are expected to be very critical of your sources, using evidence that has been well researched rather than just your own opinion or what your friends think.

Identifying the main line of reasoning in what you read or write

  • What is the main argument or line of reasoning?
  • Is the line of reasoning clear from the text?

Critically evaluating the line of reasoning for what you read or write

  • Note any statements from the text which strengthen its line of reasoning or prove the argument.
  • What statements, if any, undermine the argument?
  • Are points made in the best logical order?

Identifying hidden agendas in your sources and in your own writing

  • What hidden agendas might the writer have that might make you question the contents or conclusions of the passage? Consider what they might hope to gain through writing this piece.
  • What information might be missing that could paint a different picture?

Evaluating evidence in the text

  • What kinds of evidence or examples does the writer use? How reliable and useful is this evidence?
  • Does it really support the argument? Is the evidence strong enough?
  • Is the data up-to-date?
  • Does the text use reliable sources? What are these? What makes you think they are or are not reliable?

Looking for bias

  • Do you think there may be any bias in the text? Give reasons and examples.
  • Comment on any statistics used. Are these likely to give a true and full picture?
  • Does their writing reflect a political viewpoint?
  • Who might disagree with the writer?

Identifying the writer's conclusions

  • Does the evidence support the writer's conclusions?
  • Does the line of reasoning lead you to make the same conclusions?

Critical skills when writing

  • Apply the same rigour to your own writing as you do to analysing source materials.
  • Work out early on what your conclusion is and write this down where you can see it easily. Use this as a guide for what to read, what experiments to run, what examples to use.
  • Before you begin your main piece of writing for an assignment, write your conclusion on a piece of paper and stick this at the top of the computer. Keep referring back to this to ensure that all of your writing leads towards this conclusion. The outline plan for your writing should map out how each paragraph leads your reader towards the conclusion.
  • Ensure that your conclusion can be supported by the evidence. If you cannot find the evidence to support your position, you may need to change your conclusion.

This content has been written by Stella Cottrell, author of Critical Thinking Skills and The Study Skills Handbook.

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