Critical Thinking and Logical Fallacies

Believe it or not, Christians are to think critically. Now before you drag me off and stone me, let me remind you that there are at least two different meanings of the word “critical”. One has to do with negative criticising and condemning. That is not what I have in mind here.

The other meaning has to do with careful evaluation, testing, discerning, assessing, and judging. That is something Christians should do all the time, as Scripture makes clear:
-Proverbs 14:33 Wisdom reposes in the heart of the discerning
-Isaiah 1:18 “Come now, let us reason together,” says the LORD.
-1 Corinthians 2:15 The spiritual man makes judgments about all things
-1 Thessalonians 5:21-22 Test everything.

An important part of critical thinking is the use of logic. This is not the place to say much more about logical thinking in general, and the basic principles of logic. Instead I here want to just focus on what are known as logical fallacies. Simply stated, these come in two varieties: formal fallacies, which have to do with errors in the way an argument is put together; and informal fallacies, which have to do with errors in clarity or soundness of the reasoning process.

As to the former, let me only very briefly discuss these. Referred to as deductive reasoning, they have to do with a logical formulation, or a syllogism. Here are some basic features of a syllogism:

-A syllogism is an argument with two (or more) premises and a conclusion.
-An argument is valid when the conclusion necessarily follows from the premises. In such an argument it is logically impossible for the premises to be true and the conclusion false.
-An argument is invalid if the premises do not entail the conclusion.
-An argument is sound if it is both valid and the premises are true.

This is a sound argument:
1.  All men are mortal (major premise)
2.  Socrates is a man (minor premise)
3.  Therefore, Socrates is mortal (conclusion)

This is an invalid argument (the conclusion does not follow from the premises):
1.  All men are from Mars
2.  All women are from Mars
3.  Therefore, all men are women

This is a valid argument, but not sound, because a premise is not true:
1.  All men are from Mars
2.  Bill is a man
3.  Therefore, Bill is from Mars

This argument is valid, but not necessarily sound:
1.  God created all things
2.  Evil exists
3.  God created evil
e.g., Christians could qualify premise 1: evil is not a thing or substance, but a privation.

Informal fallacies

But for the rest of this article I want to concentrate on common informal fallacies, or mistakes in the reasoning process. There are quite a few such fallacies, but here I offer a dozen of the more common forms:

Non sequitur (Latin, “it does not follow”). An argument is a non sequitur if the conclusion does not follow from the premise. In it the conclusion can be either true or false, but the argument is a fallacy because the conclusion does not follow from the premise.

Example: The early Christians were pacifists because they did not intervene when Paul was arrested.

Attacking the person (ad hominem). An attack on the person making an argument, instead of responding to the argument itself.

“You are just a religious bigot.”
“You are homophobic.”
“Bill, you do realise that your obsession with homosexuality raises serious questions about your own sexuality.”

Begging the question (petitio principii). A type of fallacy occurring when the proposition to be proved is assumed implicitly or explicitly in one of the premises. The conclusion is snuck into the premises. It is a circular argument. It assumes what it is trying to prove.

Example: “Only an untrustworthy person would run for office. The fact that politicians are untrustworthy is proof of this.”

Category mistake. This involves comparing apples with oranges. It mixes two ideas that don’t belong together.

Example: “Just as South Africa had apartheid, so you will not allow same-sex marriage.” But skin colour or race is an innate characteristic, while sexual preference is not.

Red herring. Changing the subject to some irrelevant or different issue.

Example: You might be debating the issue of abortion, and someone throws in another issue, such as capital punishment, which is really a separate issue.

False dilemma. This involves a situation in which two alternative points of view are held to be the only options, when in reality there exists one or more other options which have not been considered.

Example: Either you support heroin injecting rooms or you want addicts to die. But in fact there is a third option. Because you love the heroin addict, and want him to live, you will seek to get him free of his heroin addiction. Getting the addict off drugs is the loving thing to do.

A straw man argument. This is a logical fallacy based on misrepresentation of an opponent’s position. You present a misrepresentation or distortion of the opponent’s position, making it easier to refute.

Example: Christians want to set up a theocracy and force people to become Christians.

The Naturalistic Fallacy. Confusing ‘is’ with ‘ought,’ or turning description into prescription.

Everyone is doing it (eg., premarital sex). Therefore, there is nothing wrong with premarital sex. So is genocide and mass murder OK because nature has floods and tsunamis?

Simple ambiguity, or equivocation. A word or phrase is used in two different senses, or with two or more meanings.

1. All sides of rivers are banks.
2. All banks have money.
3. All sides of rivers have money.

Image of Introducing Logic and Critical Thinking: The Skills of Reasoning and the Virtues of Inquiry
Introducing Logic and Critical Thinking: The Skills of Reasoning and the Virtues of Inquiry by T. Ryan Byerly (Author) Amazon logo

It is always important that we clearly define our terms in a given argument, and make sure the other side knows and accepts our meanings of the terms.

Appeal to pity (argumentum ad misericordiam). An emotional appeal that overlooks the facts of a case.

Example: “We should allow embryonic stem cell research so that Christopher Reeve can walk again.” This is not making an argument, it is appealing to our emotions.

Appeal to authority. There is a place for authority, but often it is a misplaced appeal.

“Santa Claus exists because my dad says so.”
“There is no God because Dawkins said so.”

Genetic fallacy. Confusing the origins of an idea with reasons for believing in an idea. An argument is rejected or regarded as mistaken or false because it comes from a bad or questionable source.

“You were born in Christian America, and that is why you are a Christian.” But this is irrelevant to the argument. The issue is, are there good grounds for believing in Christianity?
“You are against abortion because you are a Catholic.” Whether or not one is a Catholic is beside the point. Are there good reasons for holding that abortion is wrong?

These then are some of the more common logical fallacies. We need to be aware of these, and train our minds to spot them. Believers need to be able to think clearly, critically and logically, both as they assess other people’s arguments, and as they make their own.

Update: For further reading

There are plenty of textbooks on logic, logical fallacies, and critical thinking. Both Christians and non-Christians can benefit from them. But here are five books penned by Christians discussing the same sorts of issues. Some of the volumes cover much more than basic logic, such as Jacobs and Poythress.

T. Ryan Byerly, Introducing Logic and Critical Thinking. Baker 2017.
Norman Geisler and Ronald Brooks, Come, Let Us Reason: An Introduction to Logical Thinking. Baker, 1990.
Alan Jacobs, How to Think. Profile Books, 2017.
Vern Poythress, Logic: A God-Centered Approach to the Foundation of Western Thought. Crossway, 2013.
Douglas Wilson and N. D. Wilson, The Amazing Dr. Ransom’s Bestiary of Adorable Fallacies. Canon Press, 2017.

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12 Replies to “Critical Thinking and Logical Fallacies”

  1. The best way to sharpen yourself on these is to dialogue with leftists. They commit just about everyone of these.

    Damien Spillane

  2. Unfortunately, both Christians and non-Christians alike fall foul of these fallacies.
    Lee Herridge, WA

  3. Excellent comment Bill. I’m sure you will be familiar with a Christian classic on the subject of the exercise of the Christian mind, under that title by Harry Blamires (published 1963)
    Blamires is very stimulating and provocative, and I think John Stott may have been influenced by him to write his excellent little comment ‘Your Mind Matters’. I’m sure both are still available.
    Blamires begins with:

    “There is no longer a Christian mind. It is a comonplace that the mind of modern man has been secularised. For instance it has been deprived of any orientation towards the supernatural. Tragic as this fact is, it would not be so desperately tragic had the Christian mind held out against the secular drift …… it is difficult to do justice in words to the complete loss of intellectual morale in the 20th century church.

    There is much more in that vein of high quality comment.
    I simply quote a bit to provoke readers to check Blamires out, as I’m sure a study of his little work will be of profit to us all.

    Graham Wood

  4. 1. God created all things
    2. Evil exists
    3. God created evil (Isa 45:7 I form the light, and create darkness; I make peace, and create evil; I am the LORD, that doeth all these things.)

    – Of course, the easiest option for those who can’t accept it, is to interpret ‘evil’ as calamity or disaster, and interpret ‘create’ as allow.

    Rene Barrow

  5. Thanks Rene

    Of course my almost throw-away line was not really meant to unleash a major debate on theodicy, of which entire libraries have only begun to scratch the surface. And Augustine’s proposed partial solution is only one of many. And those wanting to take this further would also throw in texts like Jer 45:5, Zech 8:14-15, etc. Also, how one translates the Hebrew word ra is also part of the mix.

    Bill Muehlenberg, CultureWatch

  6. Hi Bill.

    A well written argument for logical thinking. So often Christians but their minds on the shelf believing they can get by with just faith or that thinking will some how show they do not have faith.

    We need to have the mind of Christ on all matters. Jesus commended the man who said to him we need to “Love the Lord your God with all your heart and with all your soul and with all your strength and with all your mind.”

    A look through a concordance will show the numerous references in the bible to using our mind.

    We can also take comfort in the promise that “If any of you lacks wisdom, he should ask God, who generously gives to all without finding fault, and it will be given to him.” James 1:5

    Keep up the good work Bill.

    Richard Jardine.

  7. Two things: 1) How heartily I agree that Christians should use their minds – how else can we “Love the Lord [y]our God with all [y]our heart and soul and mind”? In Autumn (Nov.) 2009, shortly after we returned from Aus to the UK, we went to an excellent lecture on this subject, based on the phrase in psalm 27: “The Lord is my light”; put on by the London School of Theology mainly for their graduating students. This talk may still be available through their website. 2) This is only the second of your writings/blogs I feel compelled to save as it states briefly, clearly and helpfully how to avoid/counter illogicalities. The other was your one on the Fear of God, which is a subject that has exercised me ever since, and which I will be preaching on tomorrow (uk time). Prayers would be appreciated.
    Every blessing
    Katharine Hornsby

  8. Reason is not a dirty word; but so often it ends up tainted. Why else Paul’s statements in 1 Corinthians 1 v 17 to the end of chapter 1? Verse 19 says:
    “I will destroy the wisdom of the wise,
    and the cleverness of the clever I will thwart.”
    One cannot help but think of the 18th century’s Age of Reason and all the subsequent Christians who embraced a truncated gospel because the supposed reasonableness of their beliefs, which was placed above the authority of scripture. Even closer to home, let’s point the finger back at ourselves for a minute; consider all of us who hold to the authority of scripture; but fail to live within the living reality of which the Bible speaks. We are all beggars in need of this grace, if I read – even a verse like Philippians 3 v 7 – 11 – correctly.

    Nevertheless, I do like logic and reason. These have a place for us. These can be abused by over use in the Christian experience, by Christians (e.g. evangelicals or fundamentalists) who have a tendency to always work off deductive reasoning. But logic and reason can also be abused by Christians (e.g. hyper-Pentecostals) who seek to operate almost entirely off the intuitive side or spiritual experience.

    My understanding of logic and reason (and theology and knowledge of the Bible for that matter) is that these are ways of testing experience and cannot be used as substitute for that experience. I am not into the Toronto Blessing, but in this regard I am in agreement. We cannot do without the leading of the Holy Spirit. We are called to test the Spirit’s leading. But Christian rationalism is as dead as Dorcas was.

    1 Corinthians 8 v 1 is the verse that says knowledge puffs up. Unfortunately, many of us who like to think that we employ these reasoning skills, often have problems with pride or the flesh. Many years ago I had an emotional breakdown. Many lessons were learnt; many more are yet to be. But one small outcome was that I was led to the following proverb:
    “Do you see a man who is wise in his own eyes?
    There is more hope for a fool than for him.”
    Since then this proverb has been framed and hung on my wall; a daily reminder to watch out for the puff.

    All that I have said so far, is by way of introduction to that which I wanted to respond. I was drawn in by Rene Barrow’s three point argument. In particular, point 3 took my attention. While God needs no-one to defend His character, I felt to point out two scriptures: Exodus 23 v 7 and Habakkuk 1 v 13. Related to these are the biblical themes of God’s holiness and justice. While I was not particularly drawn to Rene’s translation, I wanted to point out that if we were to accept his translation, a Christian interpretation Isaiah 45 v 7 or other similar verses, must maintain what has already been revealed about God’s character through other scriptures. In particular, I refer here to the attributes of God. God is good, just, merciful, and holy. To use a little logic (from systematic theology) we must understand a verse like Isaiah 45 v 7, in the overall context of God’s consistent goodness.

    Rene Barrow’s three point argument was also somewhat reminiscent of first year Philosophy at Uni, all those years ago. I recall a similar flaw. The argument went like this:
    Assumption 1. God is good and all powerful.
    Assumption 2. There is evil in the world.
    Deduction. 3. Therefore, either God is not all powerful, or He is not all good.
    According to logic and observation, this appears to be a sound argument.

    How is a Christian respond to it? What is the best way to deconstruct this argument? A key, I believe, is found in our Saviour’s teaching of the parable of the talents in Matthew chapter 25, especially verse 26. In this verse, in our Saviour’s parable, the master agrees with the slothful servant’s evil assessment of him. So if we are forced to make a false choice between either ‘powerfulness’ and ‘goodness,’ we have our Saviour setting the precedent by choosing powerfulness over goodness. Choosing ‘all powerfulness’ allows us to affirm enough of God to start with. We are then in a position to go on to employ what E.J. Lemmon, in his book: “Beginning Logic” calls RAA; reductio ad absurdum, a powerful form of argument which involves drawing a deduction by showing an inconsistency. The next step would be to affirm the goodness of God by demonstrating such a contradiction in the false premise which was tentatively accepted; namely that God is not all good.

    To my mind, God himself is about this action. His arguments are of a different nature. Consider the words of 1 Corinthians 2 v 2. The preaching of the cross and the work of the Holy Spirit are at the heart of this. Who is preaching the gospel like this? I want to be there.

    Christopher McNicol

  9. I have always said that any ‘educated’ person should have a working knowledge of logic, ethics and statistics. Otherwise you are a slave to propaganda and dogmatism.
    Peter Ruggles

  10. Thanks Bill,

    I enjoy, and am blessed by reading, the clear and Biblical insights of your blog. This little article is a wake up call for me; it’s time to revisit an old school text, Straight and Crooked Thinking (Robert H. Thouless), which is available on line free of charge.

    Tony Willis

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