There are a few methods for teaching critical thinking skills to public speaking and/or debate students.
One approach is to include a unit on critical thinking within a public speaking course (usually near the end) or an introduction to debate course (usually near the beginning). The unit might include Toulmin's simple framework for analyzing the claim, evidence, and warrants of arguments; it might teach students to identify informal fallacies; or perhaps the instructor gives students a checklist of basic questions to ask themselves about their arguments, e.g., "Who is the source of this information?", "How was this information collected?", etc. This approach tends to be informal (lacking strict logical rigor), simple to understand and apply, and not specific to any content domain. This is the approach I use in my debate textbook: I have an early chapter on Toulmin's framework.
Another approach is to require would-be debaters to take a separate course to improve their critical thinking skills. Some debate teams require debaters to take an additional course in logic (often in the philosophy department), which tends to be very mathematical and rigorous, perhaps even confusing, and hardly ever useful for debate contexts. I recently saw a team that requires debaters to take an additional course that surveys argumentation in different fields: legal and constitutional reasoning, political science, economics, critical theory, etc. The debaters get a primer on each topic, and some exposure to what constitutes good arguments in each field. This approach certainly gives debaters deep knowledge about various fields, but it leaves them weak on the general evaluation of new arguments in other fields.
Instead, I believe the best approach is to take the informal model but cover it as a stand-alone course (in the Communications department). I imagine this course would usually be taken by second-year debaters, but there's no reason it couldn't be open to other students as well. Perhaps the best way to organize such a critical thinking course would be:
- arguments about definitions
- arguments about facts
- arguments about cause and effect
- arguments about values
And I think the best way to treat it would be, as Neil Postman suggested in Teaching as a Subverse Activity, a collection of questions upon which to discuss. The teacher could ask framing questions, provide key readings, and open the discussion up. Here's what I envision in each section.
There needs to be a discussion about language. Specifically, students should discuss the arbitrariness of signs, the inherent ambiguity of language, and the tempting but ultimately false notion of essentialism. A simple example can spark a great discussion: "Define 'table'" or "Define 'bed'" seem so simple but become so difficult as you start to unpack it. It might even be worth starting a discussion about "discourses": how definitions are field-contextual and make sense only relative to other concepts in that field. A great example is the word "reduction" -- you should look at the Wikipedia disambiguation page to see how many different meanings there are.
The students need to discuss how to resolve definitional disputes: etymological-historical, current usage, explicit agreement, etc. It might be worth spending some time looking at Venn diagrams to compare definitions and to model syllogisms; it's good to make sure that students leave this unit clearly understanding that definitions (and syllogisms) never provide us new information about the world.
Orwell's "Politics and the English Language" makes a great transition from discussing language to discussing facts, since his main point was in how bad actors could intentional mislead with ambiguous language. It's perhaps worth having a more general discussion about the trustworthiness of sources, intentional and unintentional bias, and the appeal to authority. I've always thought it a good idea to fuse the topics of small-"m" cultural marxism and media literacy in one discussion: in other words, discuss biases of class as well as reportorial laziness, enthusiasm for expert sources (government or science), and the herd mentality. Focusing students on what isn't reported is often more effective than letting them getting bogged down in discussions about whether the stories that are reported are biased. All this is an elaboration on the trustworthiness of sources.
Getting into the nitty-gritty of the facts themselves, I think it's wise to spend time talking about the logical process of generalizing. When can we go from limited, anecdotal experience to say safely that something is usually or always true? This can lead nicely into a discussion about surveys, sampling, and statistical concepts about generalizing -- at a non-technical level. If students understand how to interpret surveys and margins of error, understand the basic logic of them, and know what to look out for (biased questions, biased sampling frames, sample size), then they're doing quite well. As a final note, Stephen Budiansky wrote a fascinating article called, "The numbers racket: how polls and statistics lie" (US News and World Report, July 11, 1988). He provides great examples of commonly circulated statistics that are just plain made up. There are books out there, too, such as Lies, Damned Lies, and Statistics that have good chapters for excerpting on this point.
Cause and Effect
First of all, it's worth discussing how statisticians and scientists set up experiments to prove cause and effect.
From logic, it's also worth discussing necessary versus sufficient causes. And, of course, the slippery slope fallacy. I like to get them diagramming causal arguments early, and once we start talking about the slippery slope fallacy, I introduce them to Ishikawa fish diagrams. I think it's also important to show them with several examples how cause and effect can easily run opposite to their intuition. A good example: kids who drink more milk have bigger feet. Is it because (a) milk causes bigger feet? (b) bigger feet cause kids to drink more milk? or (c) there's a third variable at play -- age? Self-selection is a wonderful example, too: kids who take the Princeton Review do better, on average, on their SATs. Is it because (a) Princeton Review helps? or (b) kids who take the SAT seriously also self-select to take the prep course?
From a systems perspective, students should learn a little about chaos theory (a system where initial conditions matter hugely, not one that is chaotic, thank you very much Jurassic Park), feedback loops, and the like. Economics provides a useful field here, to discuss how all the various parts of a system might push and pull on each other.
And from a real-world perspective, students should discuss what makes everyday predictions about politics, economics, and international relations credible or not. Is it reasoning by historical analogy? Is it clear analysis?
Students can get overwhelmed with the details of different philosophies, so to try to alleviate their confusion, I kept readings short (or just stick to secondary sources); I keep the number of philosophers I introduce them to at a minimum; I choose the more straightforward philosophers only. No Nietzsche, no Habermas, etc. This doesn't need to be a survey course. Instead, I frame it for them as simply as possible: "What is the right thing to do?" I tell them that the particular language and details of each philosophy are less important than understanding the philosopher's answer to my question. I stress for them that there are really only three kinds of answer to my question: (1) what some set of rules tells us is right (the dogmatists), (2) there is no such thing as a right thing to do (the nihilists); and (3) we don't know what the right thing to do is, but we do our best each time to figure it out (the pragmatists). Realizing that most moral philosophers fall into one of three temperaments is a relief. Furthermore, I make sure to bring in lots of ethical and policy dilemmas, and I encourage them to answer wearing each philosopher's hat, as it were.
For dogmatists, I might start with natural law (perhaps Aristotle or Aquinas), leading into a discussion of the appeal to nature fallacy. Of course, you also have to discuss the utilitarians, Kant, and the social contractarians (Hobbes and Rawls -- it's nice for students to see a conservative and a liberal contract view). All together that makes five philosophers to discuss, and I think it's good for students to see how one dogmatic philosophy can completely oppose another. Given an ethical or policy dilemma, it's very interesting to set up five-way debates.
For nihilists, I would tend to focus on criticisms more generally, rather than specific philosophers. There are the criticisms that no universal moral system can be formulated (but there is such a thing as justice). Then there are the moral relativists who would argue that there is no such thing as morality, period; it's just a social construct. I find that this part of the unit isn't especially interesting and one moves quickly into the pragmatists.
For pragmatists, I think I would start with a little Hume, before discussing the existentialists. (I find Sartre's ideas are fairly comprehensible to students.) Then I would move on to the "democrats": those would argue that morality should be defined by agreement and consent. Again, with two nihilistic positions (moderate and extreme) and three pragmatic positions, one can set up interesting five-way debates.
Those are my recommendations. There are good books out there that support a structure like I've suggested, such as William Hughes' excellent Critical Thinking, but I'd honestly rather piece it together with readings, real-world examples, and discussions. With a typical 12-13 week semester, that would give you three weeks per unit. Debaters would leave with a better sense of how to argue topicality (definitions), disadvantages (cause and effect), and critiques (values) -- and would hopefully be more careful researchers after the unit about facts.