- Fundamentals: Introduction to Critical Thinking
- Introduction to Critical Thinking, Part 1
- Introduction to Critical Thinking, Part 2
- Fundamentals: Deductive Arguments
- Deductive Arguments
- Fundamentals: Abductive Arguments
- Necessary and Sufficient Conditions
- Instrumental vs. Intrinsic Value
- Implicit Premise
- Justification and Explanation
- Normative and Descriptive Claims
- Fundamentals: Validity
- Fundamentals: Truth and Validity
- Fundamentals: Soundness
- Fundamentals: Bayes' Theorem
- Fundamentals: Correlation and Causation
In this video, Geoff Pynn follows up on his introduction to critical thinking by exploring how deductive arguments give us reason to believe their conclusions. Good deductive arguments guarantee their conclusions, and so must be valid (i.e., it must be impossible for the premises to be true while the conclusion is false) and have true premises. Philosophers call arguments like these "sound". You can see whether an argument is sound by trying to think of a counterexample to it, but to see whether its premises are true, you need to do some research.
Speaker: Dr. Geoff Pynn, Assistant Professor, Northern llinois University.
Speaker: Dr. Geoff Pynn, Assistant Professor, Northern llinois University.
Want to join the conversation?
- Geoff Pyn says that arguments are only valid if it is impossible for the premises to be true and the conclusion to be false.
Does this mean that ampliative arguments are always invalid?(20 votes)
- Technically yes, all ampliative argument are invalid because
1. A valid argument guarantees 100% the truth of the conclusion IF the premises are true
2. Ampliative arguments only make the conclusion probable. There's no guarantee the conclusion is true.(17 votes)
- Is any classical musician supposed to like opera. Shouldn't the premise be: Usually classical musicians do like opera? I guess opera is not the only kind of classical music?(8 votes)
- When you're trying to figure out if an argument is valid, only one thing matters: IF the premises were true, would that mean the conclusion would also have to be true? The premises themselves might be dodgy, like the claim that all classical musicians like opera, or it could even be complete nonsense. For example:
Harry Potter is a wizard.
All wizards have magical abilities.
Therefore, Harry Potter has magical abilities.
This is a valid argument. If Harry Potter is a wizard, and if all wizards have magical abilities, then Harry Potter has magical abilities. However, Harry Potter isn't real, and there's (as far as I know :P ) no such thing as wizards or magic, so none of the statements are actually true. That doesn't stop the argument from being valid.(14 votes)
- At1:59, it says "if the premises are true, the conclusion must be true." What about an argument like this:
Premise 1: one is less than two
Premise 2: two is greater than one
Conclusion: three is less than two
In this case both premises are true ,but the conclusion is false.(5 votes)
- Your argument is invalid because it is possible for the premises to be true and the conclusion false.
The following argument is valid i.e. it is impossible for the premises to be true and the conclusion false.
P1: If 1 is less than 2, then 1 is less than 3
P2: 1 is less than 2
C: 1 is less than 3
If P1 is true AND P2 is true, it is impossible for C to be false.(3 votes)
- at1:54, does it mean that something can be valid even if it is false? The concept of validity really doesn't come to me... :((3 votes)
- Yes. The thought process is valid, and it would be sound or conclusive it the premise is true.(6 votes)
- Is there a special name for an argument which has true premises, but the conclusion is false?(5 votes)
- If an argument is unsound, doesn't that mean the argument is false?(3 votes)
- Not conclusively. It could be true, but simply misstated or malformed due to a lack of speaking skills.(4 votes)
- Is not the example around4:00simply an example of denying the antecedent and therefore not a valid argument?
classical musicians appreciate opera
beyonce is not a classical musician
therefore, beyonce does not appreciate opera
Isn't that just the same as
if p then q; !p; therefore !q?
if a person is a classical musician, s/he appreciates opera
beyonce is not a classical musician
therefore beyonce does not appreciate opera(4 votes)
- I think the basic answer is that the video actually agrees the opera argument is invalid. It provides a counterexample that highlights the inadequacy of 'denying the antecedent', without specifically describing the fallacy.(2 votes)
- So at1:40, I don't understand the definition of a valid argument. So the argument can be valid (still don't understand what is meant by "valid") but the premises can be true and the conclusion false? Could someone explain in depth what a valid argument is and what the word valid in philosophical terms means?(3 votes)
I would highly recommend watching this video on validity: https://www.khanacademy.org/partner-content/wi-phi/critical-thinking/v/validity
But basically there are two important concepts when evaluating a (deductive) argument: soundness and validity.
An argument is valid if it is impossible for the conclusion to be false if the premises are true. That is IF the premises are true the conclusion must be true. It's important to note the "if" claim. A valid argument only says "if" the premises are true then the conclusion follows, there are no claims made about the premises ACTUALLY being true.
For an argument to be SOUND, it must be valid AND the premises must all be true.
Hopefully that makes sense.(2 votes)
Hi! I'm Jeff Pynn, and I teach philosophy[br]at Northern Illinois University. In my earlier Introduction to Critical[br]Thinking video, I described the difference between deductive arguments and ampliative[br]arguments. In the next few videos, I'll talk a bit[br]more about each type of argument. Let's start with deductive arguments. An argument is a set of statements, called[br]its premises, that are meant to give you a reason to believe some further statement[br]called the argument's conclusion. In some arguments, the premises are meant[br]to guarantee that the conclusion is true. Arguments like this are called deductive[br]arguments. A good deductive argument can give you a[br]very good reason for believing its conclusion. After all, it guarantees that its [br]conclusion is true. But not all deductive arguments are good,[br]and so there are several things to think about when deciding whether to believe the[br]conclusion of a deductive argument. A good deductive argument really does[br]guarantee its conclusion. Part of what this means is that its[br]impossible for the premises to be true while the conclusion is false. When this is the case, we say that the[br]argument is valid. Now this is a special, technical use of[br]the word "valid." In ordinary life, we often use this word[br]to mean something like good, cogent, or reasonable. Like if you're disagreeing with someone[br]about something, and they respond to a claim you make by saying something that[br]seems pretty reasonable to you, you might say, "Well, I guess you have[br]a valid point." Though that's what the word often means[br]in ordinary life, it's not what the word means here. When philosophers say that an argument is[br]valid, they always mean this very specific thing: that if the premises are[br]true, the conclusion must also be true. There are several other Wi-Phi videos that[br]discuss this notion of validity in more detail. To say that an argument is valid is to say[br]something about the relationship between the premises and the conclusion. Namely, that if the premises are true, the[br]conclusion must also be true. But it's not to say that its premises or[br]conclusion are true. Consider, for example, this argument. Premise 1: Beyonce was born in Paris. Premise 2: Everybody who was born in Paris[br]loves cheese. Conclusion: Therefore, Beyonce loves[br]cheese. Those premises are false. Beyonce was born[br]in Houston, and I'm willing to bet that at least some people born in Paris hate[br]cheese. Still, it's a valid argument. If the premises were true, then the[br]conclusion would have to be true. But because the premises are false, this[br]argument doesn't give you a good reason to believe its conclusion, even though it's[br]valid. Philosophers call a valid argument with[br]true premises "sound." Like the word "valid," the word "sound" is[br]term with various meanings in ordinary life, and it can be used to describe some[br]claim as reasonable or compelling. But when philosophers describe an argument[br]as sound, they always mean this very specific thing: that it's valid, and that[br]its premises are in fact true. Here's a pretty boring sound argument. Premise 1: Beyonce was born in Houston. Premise 2: Everybody who was born in[br]Houston was born in Texas. Conclusion: Therefore, Beyonce was born in[br]Texas. For more discussion of the concept of a[br]sound argument, see Aaron Ancell's Wi-Phi video entitled[br]"Soundness." So, before deciding whether to believe the[br]conclusion of a deductive argument, you need to determine whether the argument[br]is sound. And this, in turn, requires determining[br]whether the argument is valid, and whether its premises are true. Well, how do you tell whether an argument[br]is valid? Sometimes, it's just obvious. But often,[br]it's not so obvious. One way to figure out whether an argument[br]is valid is to see if you can think of a[br]counterexample to it. A counterexample is a case, either real or[br]imaginary, where the argument's premises are true,[br]but the conclusion is false. So, for example, consider this argument. Premise 1: Classical musicians appreciate[br]opera. Premise 2: Beyonce is a pop star, not a[br]classical musician. Conclusion: Therefore, Beyonce doesn't[br]appreciate opera. Now, suppose that Beyonce's been listening[br]to opera since she was a little girl, and loves Mozart's Don Giovanni. Well, then she'd appreciate opera. The conclusion would be false, even though[br]the premises would still be true. It would still be true that classical[br]musicians appreciate opera, and that Beyonce is a pop star, not a[br]classical musician. This counterexample shows that the[br]argument isn't valid, and so that even if premises are true, the[br]argument doesn't provide you with a reason to believe its conclusion. There are other, more formal techniques[br]for figuring out whether an argument is valid, which we'll hopefully be able to[br]discuss in future videos. Now, if you don't know whether the[br]premises of an argument are true, then even if the argument really is sound,[br]it doesn't give you a good reason to believe its conclusion. When you know that an argument is valid,[br]but you don't know whether its premises are true, the argument gives you, at best,[br]a conditional reason to accept its conclusion. If you learn that its premises are true,[br]then you'll have to accept its conclusion. So, how do you tell whether an argument's[br]premises are true? Well, this isn't the kind of thing logic[br]or philosophy can give you much help with. To figure out whether an argument's[br]premises are true, you need to do some research. This is one reason why being a good[br]critical thinker requires more than just logical ability. It also takes a lot of real world,[br]empirical knowledge. Unless you know enough to know whether an[br]argument's premises are true, then even if you're a really brilliant logician and[br]know that the argument is valid, it doesn't give you reason to believe its[br]conclusion. The more you know, the better you'll be[br]able to evaluate deductive arguments. Subtitles by the Amara.org community