There’s no doubt that where we’ve been has an effect on who we are. Sanctified common sense tells us not to ignore the past. But the post hoc fallacy warns us against giving too much power to the past. According to the Scriptures, the most important stuff in life flows inexorably from the human heart, not from our human histories. For all of us there’s A before B in our personal stories, but the notion that therefore A has caused B is not only illogical, it’s unbiblical.

 
The world is full of bad reasoning, which is too bad because few people bother to learn logic anymore. What’s worse, the most common logical fallacies could be learned (and memorized) without too much trouble. This could save your life, your church, and your writing a lot of trouble.

For example, everyone should be familiar with the post hoc ergo propter hoc fallacy. I say everyone should be familiar with this fallacy because everyone already is. We’ve all encountered this poor logic. I imagine we’ve all espoused it ourselves. Post hoc ergo propter hoc is Latin for “after this, therefore because of this.” It’s the fallacy that confuses temporal sequence with causation. Whenever we reason “A happened, then B; therefore A caused B,” and cite no other information to substantiate this claim, we are committing the post hoc fallacy.

We see this fallacy all the time in every day life. On Friday I was watching the Chicago Blackhawks come back to defeat the Columbus Blue Jackets. Columbus was up by a goal when their goalie allowed a relatively easy shot to get by him. A minute later the Blackhawks scored again, causing the announcers to talk throughout the rest of the game about momentum and how that easy goal got the Blue Jackets out of sync, rattled their goalie, and opened the way for the next goal. But did the first goal in any way cause the second? Maybe Columbus let its guard down, but maybe Bryan Bickell fired off a wrister that would have got passed almost any goalie.

The same kind of illogic shows up in the news just as much. I’m always hearing “The markets are responding favorably to the President’s speech this morning,” as if something as volatile and complex as the worldwide global financial markets allow for such simple cause and effect. During presidential campaigns most of the coverage revolves around the horse race, with pundits confidently explaining where every tick up or down in the polls (all withing the margin of error mind you) is the result of this gaffe or that brilliant one liner.

We like to think we know why things are they way they are. But rarely can the complexities of campaigns and markets, let alone nations and centuries, be explained by simply noting what thing came before another thing.

The Post Hoc Problem in Personal Ministry

Our particular danger as Christians is that we like to explain people with the post hoc fallacy. Though our formal theology says otherwise, our practical theology often assumes that history is destiny. When trying to help people understand their struggles and their sins we tend to mistake prior personal experiences for causality. In other words, we approach present problems as if the most helpful course of actions is always to root around in past pain. Now to be sure, a good counselor (or friend or fellow Christian) will ask good questions about our personal histories. Our past can effect the way we behave and experience reality in the present. But we mustn’t think the ways things were have determined the way things are.

In his excellent book Seeing with New Eyes, David Powlison tells the story of a young woman named Amelia. Since she was in elementary school, Amelia struggled with lesbian fantasies. She hated these fantasies and loved them at the same time. She was a Christian and figured she had to change or come out of the closet and forget about God. So she got some counseling. She discovered that she didn’t choose these desires, but they just happened to her. Her therapist accepted her (which helped) and explained the reasons for her lesbian attractions. Amelia’s father was an alcoholic and beat her and molested her. As a result, Amelia never learned to trust men. She looked to her mother for comfort, but she was helpless and passive. So Amelia has spent her life looking for a female love to fill the void her mother left inside her when Amelia needed her most. Years later, Amelia has learned that only Jesus can fill her deepest needs and she’s learning to resist her temptations more effectively.

What are we to make of this testimony? Powlison calls Amelia an “ambiguously cured soul.” Some good has certainly taken place, but there are some problems in Amelia’s story too. Her history, while crucial, is not as determinative as she thinks. Powlison notes that a woman with the same family history could have ended up with at least six different choices and habits. She could long for lesbian love, like Amelia, trying to fill the void her mother left. She could also have become promiscuous with men, having a distrust of women from her absent mother and a fascination with men from her overly sexual father. She could have become anti-social, figuring it’s not safe to relate to anyone because of her background. She could have become an addict, choosing to drown her pain in alcohol or drugs. She could have married an abusive man, repeating what happened to her growing up. Or she could have grown to love and value godliness in marriage after having seen such ungodliness growing up. Powlison concludes, “Knowledge of a person’s history may be important for many reasons (compassion, understanding, knowledge of characteristic temptations), but it never determines the hearts inclinations.”

There’s no doubt that where we’ve been has an effect on who we are. Sanctified common sense tells us not to ignore the past. But the post hoc fallacy warns us against giving too much power to the past. According to the Scriptures, the most important stuff in life flows inexorably from the human heart, not from our human histories. For all of us there’s A before B in our personal stories, but the notion that therefore A has caused B is not only illogical, it’s unbiblical.

Kevin DeYoung has been the Senior Pastor at University Reformed Church (RCA) in East Lansing, Michigan since 2004. Kevin blogs at the Gospel Coalition, and this article is reprinted with his permission.