Program / Course 26: Comprehensive Assessment / Lesson 4.1
What you will learn
- Set out an argument in standard form with numbered premises and a conclusion.
- Distinguish validity from soundness.
- Evaluate each premise for strength and name the best objection to it.
- Write a half page evaluation that treats both sides fairly.
The big idea
To evaluate an argument, write it out. List the premises, state the conclusion, ask whether the conclusion follows if the premises are true (validity), and then ask whether the premises are in fact true (soundness). Test the weakest premise hardest, and state the best objection and the best reply. The same method applies to arguments for Christian claims and arguments against them. It is a private exercise: nothing is submitted, and the student alone judges the result.
Key terms
- Premise
- A statement offered as a reason for the conclusion.
- Valid
- An argument is valid if the conclusion must be true whenever the premises are true. Validity is about form, not about whether the premises are true.
- Sound
- An argument is sound if it is valid and all its premises are true.
- Fallacy
- A pattern of reasoning that looks good but fails, such as arguing in a circle or attacking a weaker version of a view.
- Defeater
- A consideration that gives a reason to doubt a claim. A rebutting defeater argues the claim is false. An undercutting defeater argues that the reason for it is weak.
- Standard form
- A way of writing an argument as a numbered list of premises followed by the conclusion.
Background
Philosophers have long used arguments in the discussion of religion. Anselm, Aquinas, Leibniz, Hume, Kant and many modern writers have offered arguments for and against belief in God. Christians have taken different attitudes toward such arguments. Some, in the Catholic tradition especially, hold that reason can show that God exists. Some Protestants, following the Reformed tradition, hold that belief in God can be reasonable without argument. The Orthodox tradition has often been cautious about proofs of God, stressing knowledge of God in worship and experience.
Whatever the attitude, the skill of evaluating an argument is useful to all. The method has four steps. Write the argument in standard form. Check validity. Test each premise. Consider the best objection and the reply. It is helpful to remember that an argument may fail and its conclusion still be true, and an argument may succeed and a person still decline its conclusion by rejecting a premise.
This module asks for evaluation of at least four arguments, two for Christian claims and two against. The course plan asks that each be set out in standard form and given a half page evaluation of premises, strengths and weaknesses. The Stanford Encyclopedia of Philosophy entries in the library are good starting points, and the entry on fallacies is useful for avoiding common errors.
Step-by-step explanation
Step 1: Write the argument in standard form
Number the premises. Use short plain sentences. Write the conclusion after a line. For example: 1. Everything that begins to exist has a cause. 2. The universe began to exist. 3. Therefore the universe has a cause. Do not add hidden premises silently. If the argument needs one, write it down.
Step 2: Check validity
Ask: if all the premises were true, would the conclusion have to be true? If not, the argument is invalid, or it needs another premise. Do not let the plausibility of the conclusion hide a gap in the logic.
Step 3: Test each premise
Ask of each premise: what supports it, and what is the best reason to doubt it? Mark the premise you think weakest. Note whether it rests on science, history, moral intuition or a definition. Look for ambiguity: a word may shift its meaning between premises.
Step 4: State the best objection and reply
Write the strongest objection a thoughtful critic would raise. Then write the best reply that a defender would give. Decide whether the reply succeeds, and say how confident you are. If you cannot say what the other side would say, you are not ready to judge.
Step 5: Write the half page evaluation
In about 150 words, state the argument, say whether it is valid, name the weakest premise, give the best objection and reply, and say what the argument shows if it succeeds and what it does not show even then. Make this fair enough that a defender and a critic could both agree with your account of the argument.
- Can I write the argument in my own words in numbered form?
- Is it valid as written, or is a premise missing?
- Which premise is weakest, and why?
- Does any key term change its meaning between premises?
- What is the strongest objection, and what is the best reply?
- What would the argument prove if it succeeded, and what would it leave open?
Examples
Validity and soundness
All planets are made of cheese; Earth is a planet; therefore Earth is made of cheese. This argument is valid, since the conclusion follows, but not sound, since the first premise is false. (A standard teaching example.)
A missing premise
Moral values are objective. Therefore God exists. The argument needs a further premise linking objective moral values to God. A student should write it out and evaluate it. (A constructed example.)
A shift of meaning
An argument uses the word nothing in one premise to mean the absence of any thing at all, and in another to mean an empty space or a quantum vacuum. The shift can hide a fallacy of equivocation. (A constructed example.)
Different perspectives
Catholic
The Catholic tradition, following Aquinas and the First Vatican Council, holds that the existence of God can be known by reason from created things. Catholic philosophers often defend versions of the cosmological argument.
Orthodox
Many Orthodox writers hold that God is known above all by participation and experience, and are cautious about rational proofs. They do not necessarily deny that creation points to God, as Scripture says, but they place less weight on demonstration.
Protestant
Reformed epistemologists, such as Alvin Plantinga, argue that belief in God can be properly basic, that is, rational without argument. Other Protestants, such as Swinburne and Craig, defend the use of arguments for God’s existence.
Skeptical and secular
Critics such as Hume and Mackie argue that the standard arguments fail, and that the problem of evil counts against belief. Many secular philosophers hold that the debate remains open, and some regard arguments on either side as inconclusive.
Why it matters
An argument that has been written out can be examined. A student who has practiced this will also notice weak reasoning in sermons, articles and debates, including those on their own side. Evaluating arguments fairly is part of the honesty this assessment asks for.
Common misunderstandings
Misunderstanding: If an argument is valid, its conclusion is true.
Correction: Only if the premises are also true. Validity is about the logical form, soundness adds the truth of the premises.
Misunderstanding: To find a flaw in an argument is to show the conclusion false.
Correction: A conclusion may be true even if a given argument for it fails. A flaw removes one reason, not every reason.
Misunderstanding: Philosophical arguments are meant to compel belief.
Correction: Few philosophers claim that. Arguments can give reasons and raise or lower confidence, and people differ on how much they carry.
Knowledge check
What is the difference between valid and sound?
A valid argument is one where the conclusion must be true if the premises are. A sound argument is valid and also has true premises. An argument can be valid and unsound if a premise is false. Evaluation therefore asks about form first and then about the truth of each premise.
Why should an argument be written in standard form?
Writing the premises as numbered, plain sentences exposes hidden assumptions, shifts of meaning and gaps. It lets the student point to the exact premise that is weak instead of saying that the argument seems wrong. It also makes fair comparison with the objections easier.
Does the failure of an argument disprove its conclusion?
No. An argument may fail for a bad premise or a gap while the conclusion is true for other reasons. A fair evaluation says what the failure shows, namely that this reasoning does not establish the conclusion, and leaves the question open or points to other arguments.
What belongs in a half page evaluation?
The argument in standard form or a summary of it, a judgment on validity, the weakest premise, the strongest objection and the best reply, and a statement of what the argument would show if it worked. The tone should be fair enough that both defenders and critics accept the description.
Think it through
- When did you last change your mind because of an argument?
- Do you apply the same standards to arguments you like and those you do not?
- What does it mean to hold a belief without an argument for it?
- How could you tell whether you were being fair to an opponent?
Independent assignment
Evaluate one argument
In your own notebook, choose one argument for or against a Christian claim. Write it in standard form, judge validity, name the weakest premise, give the strongest objection and best reply, and write a half page evaluation of about 200 words. Do not send this to anyone or post it anywhere.
Further study
- Stanford Encyclopedia of Philosophy, Fallacies For avoiding common errors in reasoning.
- Stanford Encyclopedia of Philosophy, Cosmological Argument An overview of cosmological arguments, with objections.
- Alvin Plantinga, Warranted Christian Belief On whether belief in God needs argument.
- Richard Swinburne, The Existence of God A cumulative case argument to read critically.
- Stanford Encyclopedia of Philosophy, Hume on Religion A major critic’s approach, to read alongside the defenders.
- 1 Peter 3:15 On giving a reason for hope with gentleness and respect.