Wikipedia provides a reasonable definition of critical thinking:
Critical thinking is purposeful and reflective judgment about what to believe or do in response to observations, experience, verbal or written expressions, or arguments. Critical thinking might involve determining the meaning and significance of what is observed or expressed, or, concerning a given inference or argument, determining whether there is adequate justification to accept the conclusion as true.
Critically evaluating assertions, arguments, and proposals, whether presented orally or in print, is an important comprehension skill. Many personal, professional, and social decisions are based on what we are told by other people. Because faulty arguments and propaganda are so common, critical thinking has a role in almost every important decision we make.
The consensus is that the typical K-12 education does not result in students with good critical thinking skills. I agree with this consensus.
What I do not agree with; however, is the notion that critical thinking is some generalized skill that is independent of domain knowledge.
Let's see why this is so by looking at skills needed to critically read a passage of text. I am going to use the procedure outlined in Direct Instruction Reading, 4th edition, chapter 22, which is a simplified version of the skill suitable for elementary school students, but, which sadly most students never acquire.
The four steps in the critical-reading process can be treated as the major component skills:
(1) identify the author's conclusion; that is, what does the author want the reader to believe?
(2) Determine what evidence is presented; that is, what does the author present to convince the reader? Evidence or opinion?
(3) Determine the trustworthiness of the author, that is, can the reader trust what the author says?
- Does the evidence come from a qualified person?
- Does the person have biases?
(4) Determine if the conclusion derives from the evidence. Identify any faulty arguments.
- Tradition, either old or new (sometimes called a bandwagon effect)
- Improper generalization
- Confusing correlation with causation (or coincidence)
Those who think critical thinking/reading is a generalized skill are confusing the general procedure with the act of performing the procedure itself. A student might have learned the procedure, but be unable to perform the procedure adequately for a particular text. That's where domain knowledge comes into play.
The best way to see this is by way of example. So, let's use the procedure to critically read a typical passage that students might encounter.
Thomas Edison, the inventor of the lightbulb, was seriously concerned about the increasing use of alternating current as a form of electricity. Edison believed that because alternating current involved so much more current than direct current, alternating current was a threat to the nation. Many fires were caused by alternating currents. In fact, alternating current was used in Sing Sing to electrocute criminals. Direct current was used with light bulbs for many years. Edison felt direct current was still the best form of electricity.
Another example of the dangers of alternating current has just occurred. A house wired with alternating current caught fire and burned to the ground. The fire started when an electrical wire became so hot that a wall caught fire. Alternating current will eventually cause a fire whenever it is used. Direct current rather than alternating current should be used for lighting.
The Daily Post used direct current to light its press room for over a year. Reporters are much happier now. They write more interesting stories. Sales of the newspaper have increased dramatically. The Daily Post is now the most popular newspaper.
Identify the Author's Conclusion
First the students must use details from the passage (seriously concerned, a threat to the nation, direct current is still the best) to form a main idea (or author's conclusion). Identifying an author's conclusion is a continuation of summarization skills.
Right off the bat you can see that critical reading/thinking is dependent on domain knowledge and the student's ability to extract the author's conclusion from the text and justify that conclusion with supporting details from the text. A student might be able to extract the main idea from Dr/ Seuss's Green Eggs and Ham, but be unable to extract the main idea from one of Plato's Dialogues. If critical thinking/reading were a generalized skill, then this wouldn't be the case. The student's inability to identify the author's conclusion will impact his ability to perform the remainder of the procedure.
Discriminating Evidence from Opinion
The second step is for the student to decide whether the author's conclusion is based on opinion or evidence. If it is based on opinion, students must understand that the conclusion is nothing more than a suggestion by the author about what people should think. A conclusion based on opinion does not imply that the student should believe or act on it.
In the example passage, both opinion and evidence are used to support the author's conclusion. The statement that alternating current is a threat to the nation is opinion. The other details are evidence used to justify the author's conclusion (occurrence of fires, electrocution of criminals, initial use of direct current as an energy source.)
This step is also intertwined with domain knowledge. Being able to discriminate between fact and opinion requires that you understand the underlying statement in the first place.
Fact or opinion?
In my judgment, the total enthalpy of any non-isolated thermodynamic system tends to decrease over time, approaching a minimum value.
It's not an opinion, even though it uses a phrase ("In my judgment") that typically indicates opinion. It is evidence. The statement is the second law of thermodynamics. But, you wouldn't know this unless you knew thermodynamics, and, thus, you wouldn't be able to discriminate between opinion and evidence.
In actuality the statement is inaccurate evidence. The statement is not the second law of thermodynamics; I changed some of the terms to make it inaccurate. Again, you wouldn't know this unless you knew thermodynamics.
Determining the Trustworthiness of an Author
The third step consists of several questions, all relating to the reliability or trustworthiness of the person presenting the argument.
Question (a) is whether the evidence comes from a qualified person. Since Edison was definitely an expert on electricity in the late 1800s, he was qualified.
Again, this determination requires that you know something about Thomas Edison. That's domain knowledge.
Question (b) concerns biases the expert might have. In Edison's case, two major biases existed. One was his deep personal and involvement in a company that provided direct current. He stood to lose money if alternating current replaced direct current. Also, his reputation was at stake. He became famous, in part, because of his discovery of the lightbulb and a distribution system for electricity based on the use of direct current. If alternating current replaced direct current, his reputation might be diminished.
Again, we need domain knowledge knowledge to make the determination.
Since Edison's biases contribute to the passage's conclusion, the evidence he cites may not be trustworthy.
Since there is doubt about the trustworthiness of the author, students must seek information from different experts. The statement that direct current is the best form of electricity is disputed by many experts. Alternating current can be transmitted great distances, but direct current cannot (at least during the relevant period). If remote areas are to receive electricity at a reasonable rate, alternating current is a necessity.
So, since the expert is biased and alternate interpretations of the evidence are compelling, the evidence is probably not trustworthy.
Again, the student must know quite a bit about electricity and its ability to be transmitted to make seek out the appropriate sources and understand the information presented. take a look at this article on electric power transmission and see if you can make sense of the differences between direct current transmission and alternating current transmission. And then you have to be aware of the history of electric power transmission to understand that the information this article presents was unknown during the time that our passage was written. But, how would you know this without quite a bit of domain knowledge in both electricity and the history of electrical power transmission? Google may be your friend, but he's not this good of a friend for you.
Identifying Faulty Arguments
The final step in the critical-reading process is deciding whether a conclusion legitimately derives from the evidence. In many arguments, valid evidence will be presented, but then a conclusion will be drawn that does not derive from the evidence. In the alternating-current example, one possible interpretation is that since direct current has been used with lightbulbs for many years, it should continue to be the best form of electricity. This faulty argument illustrates the use of tradition: what has been the best must continue to be the best. Conclusions based on tradition are not necessarily true. What has worked well may continue to be the best procedure, or a better procedure may be developed. Students can disregard conclusions based on tradition. (Note that the same attitude can be taken toward newly developing traditions; i.e., "Everybody is starting to use alternating current; therefore, you should, too." A conclusion that a product or procedure is better because it is popular is faulty.)
In the second paragraph, there is an example of improper generalization. One valid example is presented, but then a conclusion is drawn that applies to all examples. One fire caused by alternating current does not mean that alternating current will cause a fire every place it is used. Improper generalization occurs often: "I saw a rich person who was rude. What makes rich people rude?" "We sat next to a long-haired man in the movies. He smelled. I'll bet he hadn't bathed in weeks. Long-hairs should take better care of their bodies."
The third paragraph involves a confusion of causation and correlation. An event that is associated with success or some other positive outcome through coincidence is erroneously concluded to be the cause of the positive outcome.
Direct-current lighting is associated with happier reporters, more interesting stories, and greater sales; however, direct current did not necessarily cause reporters to be happier. The electric lighting that produced the positive outcomes could have been achieved with direct or alternating current. Conclusions suggesting causation that are, in fact, based on correlation can be disregarded. Confusion of correlation and causation is often made: "Joe Blow uses Squirt-Squirt deodorant, and girls always chase him." "Sally took You-Bet-Your-Life vitamins every day. She lived to be 106."
Of course, there are many other logical fallacies and faulty arguments that the student should know, but these three are a good start for primary grade students since they are among the most common.
Sadly,this last step is often completely ignored in most schools. Most students are simply not taught how to identify faulty arguments at all. And let me be crystal clear here: it should be taught. And, I'm guessing that the reason why it isn't taught more often, or at least learned by most students, is because it is the culmination of basic reading instruction which is rarely reached by many students.
Many students never learn how to decode accurately and proficiently in grade-level texts. This is criminal, quite frankly, because this is something we have known how to effectively teach for some time now. Then students need to comprehend what they've decoded well enough to extract the main idea and the justifications therefor. Most students can't do this competently when the main idea is presented to them as an alternate in a multiple choice format, much less being able to generate one on their own. And, if a student can't do this initial step in critical reading, how is she going to accomplish the accomplish the remaining steps which require an understanding of the author's conclusion in the first place?
So, what we have is two separate problems. One problem is that students are often not taught how to spot faulty arguments and logical fallacies which are important skills needed to think and read critically. No one seriously disputes that this is a problem. These skills should be taught. Period.
But, even if students are taught these skills, they will not necessarily be able to think and read critically because knowing how to identify and distinguish faulty arguments and logical fallacies is not the same thing as critically thinking/reading as many proponents of 21st Century skills seem to think. Critical thinking/reading involves much more than identifying faulty arguments, as I described above. And, the ability to identify faulty arguments is not the generalized form of critical thinking as some seem to think.
There is another problem that must also be dealt with. That problem is that students can't comprehend well enough to extract the author's conclusion, to discriminate evidence from opinion, and to determine if the author is trustworthy. All of these skills require and are a function of the student's domain knowledge. You have to know a lot of stuff, to think about a lot of stuff.
This is just a roundabout of saying that there are prerequisites to being able to think/read critically that also need to be addressed (and have never been adequately addressed) before students can make use of the "21st century skills" many think are important, like being able to identify faulty arguments and logical fallacies.
What's the sense of teaching a student astrophysics if the student doesn't know how to do basic arithmetic or understand basic science? Perhaps this is why schools haven't traditional taught these things in the first place.