The National Public Radio show Fresh Air just ran a pair of interviews with two scientists talking about whether God exists. The conversations touch on a lot of things we've been discussing in class.
Hey, where's the interview with an agnostic? The media are so biased toward those with opinions.
Showing posts with label as discussed in class. Show all posts
Showing posts with label as discussed in class. Show all posts
Thursday, March 29, 2007
Thursday, March 22, 2007
Review: Deductive Soundness
DEFINED: A deductive argument is sound when:
(1) the argument is valid; and
(2) all the premises are true.
WHAT IT MEANS: This is the gold standard—as good as it gets for a deductive argument. From the start, a sound argument has to be valid. But on top of it, each premise must also be true.
So to test for soundness, we first do our validity test. We do the imagine-a-world test. If the arg fails this test, then it's invalid, and automatically unsound.
If it passes the validity test, then we need to check the actual truth of the premises. So we forget about the imaginary world, and come back to the real world. Are all of the premises actually true in the real world, or is one or more false or questionable (opinionated)? If they're all true, then the argument is sound. If one or more is false or questionable, then the argument is unsound.
An argument is unsound if it is not sound. (duh) But remember, it’s easy for an argument to be unsound. Only one of many things has to go wrong for an argument to be unsound. One false premise, and it’s unsound. One false move in an argument that makes it invalid, and it’s unsound.
(1) the argument is valid; and
(2) all the premises are true.
WHAT IT MEANS: This is the gold standard—as good as it gets for a deductive argument. From the start, a sound argument has to be valid. But on top of it, each premise must also be true.
So to test for soundness, we first do our validity test. We do the imagine-a-world test. If the arg fails this test, then it's invalid, and automatically unsound.
If it passes the validity test, then we need to check the actual truth of the premises. So we forget about the imaginary world, and come back to the real world. Are all of the premises actually true in the real world, or is one or more false or questionable (opinionated)? If they're all true, then the argument is sound. If one or more is false or questionable, then the argument is unsound.
An argument is unsound if it is not sound. (duh) But remember, it’s easy for an argument to be unsound. Only one of many things has to go wrong for an argument to be unsound. One false premise, and it’s unsound. One false move in an argument that makes it invalid, and it’s unsound.
Review: Deductive Invalidity
DEFINITION: A deductive argument is invalid when the truth of the premises does NOT guarantee the truth of the conclusion.
WHAT IT MEANS: If an argument isn’t valid, it is invalid. This means that you can’t draw the conclusion from the premises – they don’t naturally follow. Invalid arguments do not preserve truth.
EXAMPLES:
1) All humans are mammals.
All whales are mammals.
All humans are whales.
2) If it snows, then it’s below 32 degrees.
It doesn’t snow.
It’s not below 32 degrees.
3) All humans are mammals.
All BCC students are mammals.
All BCC students are humans.
4) Either Yao is tall or Spud is short.
Yao is tall.
Spud is short.
Even though arguments 3 and 4 have all true premises and a true conclusion, they are still invalid, because their form is bad. Argument 3 has the same exact structure as argument 1—a bad structure (it doesn’t preserve truth).
Even though in the real world the premises and conclusion of argument 3 are true, we can imagine a world in which all the premises of argument 3 are true, yet the conclusion is false. For instance, imagine that BCC starts letting whales take classes. The second premise would still be true, but the conclusion would then be false.
The same for argument 4: even though Spud is short (Spud Webb is around 5 feet tall), this argument doesn’t guarantee this. The structure is bad (it’s either this or that; it’s this; therefore, it’s that, too.). We can imagine a world in which Yao is tall, the first premise is true, and yet Spud is tall, too.
WHAT IT MEANS: If an argument isn’t valid, it is invalid. This means that you can’t draw the conclusion from the premises – they don’t naturally follow. Invalid arguments do not preserve truth.
EXAMPLES:
1) All humans are mammals.
All whales are mammals.
All humans are whales.
2) If it snows, then it’s below 32 degrees.
It doesn’t snow.
It’s not below 32 degrees.
3) All humans are mammals.
All BCC students are mammals.
All BCC students are humans.
4) Either Yao is tall or Spud is short.
Yao is tall.
Spud is short.
Even though arguments 3 and 4 have all true premises and a true conclusion, they are still invalid, because their form is bad. Argument 3 has the same exact structure as argument 1—a bad structure (it doesn’t preserve truth).
Even though in the real world the premises and conclusion of argument 3 are true, we can imagine a world in which all the premises of argument 3 are true, yet the conclusion is false. For instance, imagine that BCC starts letting whales take classes. The second premise would still be true, but the conclusion would then be false.
The same for argument 4: even though Spud is short (Spud Webb is around 5 feet tall), this argument doesn’t guarantee this. The structure is bad (it’s either this or that; it’s this; therefore, it’s that, too.). We can imagine a world in which Yao is tall, the first premise is true, and yet Spud is tall, too.
Review: Deductive Validity
Here's a review of the tricky term "valid" as it refers to deductive arguments:
DEFINED: A deductive argument is valid when the truth of the premises guarantees the truth of the conclusion.
WHAT IT MEANS: Validity focuses on the form or structure of the argument. If an argument is valid, then it has good form – truth preserving form.
Basically, if we assume that all the premises are true, then the conclusion must also be true for an argument to be valid. Notice we are only assuming the truth of the premises, not checking to see whether they are actually true. Again, this makes sense, because we’re truth-preservers: if the premises are true, the conclusion that follows must be true.
EXAMPLES:
(1) All humans are mammals.
All mammals have hair.
All humans have hair.
(2) If it snows, then it’s below 32 degrees.
It snows.
It’s below 32 degrees.
(3) All humans are mammals.
All mammals have wings.
All humans have wings.
(4) Either Yao is tall or Spud is tall.
Yao is not tall.
Therefore, Spud is tall.
Even though arguments 3 and 4 are ultimately bad, they are still valid—their form is good. The second premise of argument 3 is false—not all mammals have wings—but it has the same exact structure of argument 1—a valid structure. Same with argument 4: the second premise is false (Yao Ming is about 7 feet tall), but the structure is good (it’s either this or that; it’s not this; therefore, it’s that).
To evaluate validity, then, assume that all the premises are true. Imagine a world in which all the premises are true. In that world, MUST the conclusion also be true? Or can you imagine a scenario in that world in which the premises are true, but the conclusion is still false? If you can imagine this situation, then the argument is not valid. If you cannot, then the argument is truth-preserving (inputting truths guarantees a true output), and thus valid.
IMPORTANT: Individual sentences are true or false. Arguments are valid or invalid.
DEFINED: A deductive argument is valid when the truth of the premises guarantees the truth of the conclusion.
WHAT IT MEANS: Validity focuses on the form or structure of the argument. If an argument is valid, then it has good form – truth preserving form.
Basically, if we assume that all the premises are true, then the conclusion must also be true for an argument to be valid. Notice we are only assuming the truth of the premises, not checking to see whether they are actually true. Again, this makes sense, because we’re truth-preservers: if the premises are true, the conclusion that follows must be true.
EXAMPLES:
(1) All humans are mammals.
All mammals have hair.
All humans have hair.
(2) If it snows, then it’s below 32 degrees.
It snows.
It’s below 32 degrees.
(3) All humans are mammals.
All mammals have wings.
All humans have wings.
(4) Either Yao is tall or Spud is tall.
Yao is not tall.
Therefore, Spud is tall.
Even though arguments 3 and 4 are ultimately bad, they are still valid—their form is good. The second premise of argument 3 is false—not all mammals have wings—but it has the same exact structure of argument 1—a valid structure. Same with argument 4: the second premise is false (Yao Ming is about 7 feet tall), but the structure is good (it’s either this or that; it’s not this; therefore, it’s that).
To evaluate validity, then, assume that all the premises are true. Imagine a world in which all the premises are true. In that world, MUST the conclusion also be true? Or can you imagine a scenario in that world in which the premises are true, but the conclusion is still false? If you can imagine this situation, then the argument is not valid. If you cannot, then the argument is truth-preserving (inputting truths guarantees a true output), and thus valid.
IMPORTANT: Individual sentences are true or false. Arguments are valid or invalid.
Tuesday, March 13, 2007
Think [Tap-Dance] God
There's a philosophy comic strip that is running a whole series on the ontological argument that god exists. Here are the comics:
If you're still jonesing for the a priori, there's also this entry on ontological arguments in the Stanford Encyclopedia of Philosophy.
If you're still jonesing for the a priori, there's also this entry on ontological arguments in the Stanford Encyclopedia of Philosophy.
Thursday, February 22, 2007
Innate Ideas: I've Had a Few
Here are a couple articles by Steven Pinker that offer some psychological insights on the innate ideas debate we discussed in class:
But hey, why read when you can watch a video? With that in mind, here's his appearance on The Colbert Report (the second part is particularly relevant to innate ideas):
Pinker has a few books on this stuff, and a lot of other interesting articles, too.
But hey, why read when you can watch a video? With that in mind, here's his appearance on The Colbert Report (the second part is particularly relevant to innate ideas):
Pinker has a few books on this stuff, and a lot of other interesting articles, too.
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