Logic 101 — Introduction

This is the first post in a series on logic. In discussions on many diverse topics, it’s common to discover errors in critical thinking. Why is this important? It surprises people to learn the church will be infested with false teachers who — either from maliciousness or ignorance — lead astray many people.

But there were also false prophets among the people, even as there will be false teachers among you, who will secretly bring in destructive heresies, even denying the Lord who bought them, and bring on themselves swift destruction. And many will follow their destructive ways, because of whom the way of truth will be blasphemed. (2 Peter 2:1–2 NKJV)

Heresies thrive on the inability of people to think clearly and analyze correctly. As Paul said, be a Berean and search daily to see if what you’re hearing is true.

Sadly, many pew-warmers exist swallowing any poison coming their way, as long as Friday’s pot-luck was good. Paul warned Timothy about exactly such a time.

For the time will come when they will not endure sound doctrine, but according to their own desires, because they have itching ears, they will heap up for themselves teachers; and they will turn their ears away from the truth, and be turned aside to fables. (2 Timothy 4:3–4)

In other words, Paul told you to be a healthy skeptic.

Logic provides the tool to get the job done, avoid heresy, ripoffs, and understand why what you believe is true.

If you’re (ahem) youth-challenged, you might recall the old Camel cigarette ad, asking the question “What cigarette do you smoke, doctor?” And the brand named most, was Camel. Yes, according to a survey, more doctors smoke Camels, than any other cigarette.

Today we laugh at the absurdity of the ad. Yet back in the day, it likely was quite effective.


The ad appealed to someone who should know — doctors — and the idea many of them agreed on the best cigarette.

Appealing to your sense of (misguided) reason (not logic), the ad contains several logical mistakes, specifically the argument from majority and argument from authority errors (which we’ll discuss later, don’t worry).

History is filled with logical errors — everything from Piltdown man to flat earth.

But first, we must define terms. What is logic?

Common Sense

Common sense isn’t logic, but reason, and the two can be easily confused.

For example, when speaking to an atheist I pointed out the logical absurdity of atheism, he responded with “but theism isn’t?”. He confused logic with common sense — in his eyes God violated common sense, and was thus illogical.

As another example, many hold the strange idea Isaiah didn’t write the book bearing his name — the so-called deutero-Isaiah hypothesis. The idea comes from analyzing the style of different sections, and concluding some amount of differences proves different authors.

The theory says at least three guys existed: The guy who wrote the first half, the second half, and the guy who compiled it.

They have no reason (other than their guess) to believe those guys existed, they don’t know who they were, or why they did what they did.

The only reason to believe three mysterious people exist is because their theory (multiple authors) demands it.

That violates common sense and sound research.


Logic uses defined rules to arrive at an answer. It’s similar to mathematics. If you see the expression (2 + 3) X 5 + 1 = ? you understand how to correctly compute the answer because mathematics uses clearly defined rules.

Some might say in violation of common sense, but in the end if mathematical rules are followed, everyone understands the answer will be correct.

Logic allows you to follow a defined path, and arrive at a valid answer. It is not necessarily a proof, however.

In the atheism vs theism discussion, we have no need to discuss atheism, as it contains nothing but immature gibberish, like the sentence chimney yes the beneath.

Atheism is illogical for the simple reason you can’t say God doesn’t exist unless you posses all knowledge. If you don’t, God can exist outside your knowledge.

atheism diagram

“A” represents your knowledge, while all knowledge by “B.” No matter how large “A” becomes, it will never be as large as “B,” thus God could exist anywhere outside the box of your knowledge unknown to you.

That’s why atheism is immature gibberish. No reason exists to even discuss it. I’ve talked to many so-called atheists, and I’ve yet to meet one who actually is an atheist, for the simple reason most understand the failed logic of atheism.

Only someone who does not understand logic could hold to atheism.

Theism, however, is logical; it does not prove God exists, only that theism follows logic and is rational.

Logic and critical thinking remains vital, whether you’re discussing politics, mathematics, atheism, or Christianity.

Let’s briefly use logic to solve a centuries old issue — can you lose your salvation?

One tactic in logic is indirect proof. Begin with a statement you don’t know the truth of, deduce from it, and if you arrive at a contradiction, your original statement must be false.

Let’s assume you can lose your salvation. What does that imply? Your salvation is not eternal, it can come and go.

Wait, doesn’t the Bible speak about eternal salvation? What does eternal mean? Forever. If you can lose it, it’s not forever, which is a contradiction, thus the original idea (you can lose your salvation) must be in error.

Using logical methods, no need exists to visit the proof-texts one side or the other uses.

Failure to follow logic can lead you into all sorts of problems, from economic disaster to heresy.

You don’t want that, do you?

Filed Under: Logic

Recommended Citation:
Yeager, Darrin "Logic 101 — Introduction" (2023-11-23 14:45),
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