Notes for Think Again: How to reason and argue (Lectures 3 Validity and Soundness)

These are my course notes for the Coursera course "Think Again" by Walter Sinnott-Armstrong at Duke University and Ram Neta at University of North Carolina.

This follows on from my earlier notes.

VALIDITY

Remember that arguments consist of premises and conclusions, and these are supposed to be related in a good argument. We need some standards for evaluating arguments (so we can deconstruct, reconstruct and create our own). Two standards for evaluating arguments are 'Valid' and 'Sound'.

There are 2 main reasons for arguments to go wrong:

• One or more premises are wrong or false
• The premises do not provide a good reason for the conclusion

Remember the relation between premises and conclusions.

• DEDUCTIVE: Conclusion follows from the premises. Trying to be valid.
• INDUCTIVE: Argument is not supposed to be valid. Conclusion does not follow from premises.

The rule for validity is:

An argument is valid if and only if it is not possible that both all of its premises are true and its conclusion is false

This means that there can be no way both premises come out true when the conclusion is false. This stands if you assume that the conclusion is false and then test the premises; if they still remain true while the conclusion is asserted false, then it is NOT a valid argument.

This test helps us determine if the premises actually support the conclusion. Another way to look at it is that an argument is valid if and only if whenever its conclusion is false, at least one premise must also be false.

A valid argument is not:

•  necessarily good. An argument can be valid but be no good at justifying or explaining the conclusion
• dependent on whether the premises and the conclusion are actually true. It is only dependent on what is possible.

Validity in this context is simply a technical term. Validity should not be confused with other types of validity.

SOUNDNESS

A sound argument is one where the conclusion must be true.


An argument is sound if and only if:

• all of its premises are true
• it is valid

If the premises are true and the argument is valid, then the conclusion must be true because if it is false then one or more of the premises must also be false (as per the conditions of validity).

If a deductive argument is not sound, then it is not a good argument (because a deductive argument is trying to be valid, with the conclusion following from it's premises).

BASICS OF RECONSTRUCTION

The goal of reconstruction is to put an argument in a form in which we can easily and accurately assess it in as fair a manner as possible.

1. Do a close analysis
2. Remove all excess verbiage
3. List all explicit premises and conclusion in standard form
4. Clarify where needed (Sharpen edges)
5. Break up where possible without distortion
6. Divide the argument into sub-arguments, and arrange them in order
7. Assess whether each argument is valid
8. Add suppressed premises where needed
9. Check each premise for truth
10. Qualify premiese to make them true where needed if possible
11. Assess the argument.

If we manage to reconstruct a sound argument, we know that the conclusion is true. If it is unsound, is it the fault of the argument or ourselves because we didn't understand the argument?

Excess verbiage includes:

• People repeating themselves for rhetorical effect, stalling for time, or filling in the time
• Road markers -> help keep track of an argument (what we are talking about, and why). They don't offer anything additional to the argument. Includes changing topics.
• Tangents -> anecdotes and stories that make the argument interesting or memorable, but offer no reasons for the argument. They can also try to fool or distract you (red herring)
• Examples -> trying to highlight or bring to home the point of the argument. However, the example may just be an outlier. It can sometimes be used as a premise for the argument.

You need to be careful when removing excess words (including assuring, guarding and other words), because if you remove too much you may make the argument worse and not true to the intentions of the original speaker.