Shall We Reason Together? Part Seven: Probability and the Limits of Logic

I have been arguing against a philosophical theory that denigrates reason by stating that inferences drawn from Scripture are always lower in authority than the straightforward declarations of Scripture. I have attempted to show that this theory is bad philosophy, bad exegesis, and bad theology. Necessary inferences drawn from Scripture are just as authoritative as the Scriptures themselves.

Now it is time to back up and to discuss certain conditions that necessarily limit the usefulness of logic when understanding the Scriptures. Within those limits, logic is necessary, useful, and in at least some instances, unerring. Outside of those limits, logic can become a tool with which we deceive ourselves and others. It is important for us to know where those limits are.

The first condition has to do with the distinction between deductive and inductive reasoning. In deductive logic, the conclusions arise necessarily from the premises. When a deductive syllogism is valid and the premises are true, the conclusion must without exception be true. Inferences that are drawn by strict induction (a valid syllogism) from biblical propositions (true premises) are always true and must be just as authoritative as the Scriptures themselves.

For example, Scripture nowhere teaches the doctrine of the Trinity in so many words. What the Bible teaches in various places is that God is One; that the Father, Son, and Holy Spirit each are God; and that these three are somehow distinct from each other. When we reason deductively from these truths, we derive the doctrine of one God in three divine persons.

The same is true of the hypostatic union. The formula of Chalcedon is not found in the New Testament. Rather, the New Testament shows in one place that Jesus is truly God; in another place that He is truly Human; in yet another place that He is one person. It is by reasoning from these truths deductively that we define the two-natures-one-person dogma.

Neither the Trinity nor the hypostatic union is stated in so many words anywhere in the Bible. Nonetheless, for orthodox Christians these doctrines are as authoritative as any biblical statement. They are rightly regarded as fundamentals of the faith. One reason that they are so authoritative is that they are necessary inferences, conclusions that are unavoidable in the light of biblical revelation.

Most theological and ethical arguments, however, are inductive rather than deductive. They may even alternate between the two methods. In an inductive argument, we draw inferences that are not necessary. They are merely probable. Their degree of probability limits the extent to which we ought to press their authority.

In my opinion, the Bible teaches premillennialism, but not with deductive certainty. The premillennial theory is, at best, probable (I think quite probable, given the way that I view the evidence—but still only probable). Pretribulationism, while still probable (in my opinion), is less certain than premillennialism. The identity of the sons of God in Genesis 6 is only marginally probable—and on that point I am not even revealing my own view!

One must not confuse certainty with authority. God’s Word teaches exactly one view of the nature of the millennium, the timing of the rapture, and the identity of the sons. Whichever view is taught in Scripture is absolutely authoritative. Our problem, however, is that we are only relatively sure which view the Bible teaches.

What are the consequences of this uncertainty? When our conclusions are merely probable, we must hold ourselves ready to reexamine them in the light of new information or new perspectives. We should be conscious of (and willing to state) the conditions under which our minds could be changed. We should advocate our conclusions, but only with the force that their probability warrants. We should be willing to recognize the strength of the evidence that counts against our own conclusions. We should be fair with those who disagree with us—in fact, we should be able to state their position as well as they themselves do. We ought to exhibit charity toward those who disagree with us, displaying evenness in our responses. In short, we must manifest a spirit of genuine humility while advocating the conclusions that we believe are reasonable in light of the evidence.

Of course, most of these attitudes should characterize the work of the mind under all circumstances. Docility (teachability) is a virtue that we must never outgrow. Furthermore, the key difference between instruction and indoctrination is the willingness to tell the whole story, i.e., to expose ourselves and others to conclusions that we think are incorrect, and to appreciate the evidence that supports those conclusions—even at the risk of changing our minds.

Most of the ethical and theological conclusions that we draw from the Scriptures are inductive, and consequently they are probable in nature. We should recognize our lack of certainty about these inferences. Lacking certainty, we should hold our conclusions humbly. That does not imply, however, that we should become timid about drawing inductive inferences.

Some individuals are reluctant to reach a conclusion unless they can hold it with certainty. In the absence of overwhelming evidence, they defer judgment indefinitely. Such timidity is as great an error as arrogance. God would not speak to an issue if He did not intend to communicate something to us, and He would not communicate if He did not expect us to understand. We must try to reach some conclusion, even when Scripture is not as clear as we would like.

Furthermore, as long as we advance them humbly, we do not need to be afraid to advocate such conclusions. Indeed, we must: the truth is authoritative, even if we grasp it only imperfectly. God’s sovereignty obligates us to believe and to practice what we believe God has said, and Christian charity obligates us to seek to convince our brethren of whatever we think is true. The same is true of our brethren, and we should not take offense when we find them seeking to convince us of what they believe to be true. Rather, we should be grateful for such a demonstration of their brotherly love.

Necessary inferences drawn from biblical premises are just as authoritative as the text of Scripture itself. A necessary inference is one that is drawn through valid arguments from true premises. Conclusions drawn inductively rather than deductively are probable rather than necessary. Probable inferences should generally be advanced with greater caution. They should be advocated only as strongly as the probability that they are true.

This rule of thumb prompts a question. Are there any instances in which inductive inferences could and should be advocated as strongly as deductive ones? This is an important question, and it concerns some of the core of the Christian faith. Therefore, I want to take a brief detour to answer it. Afterwards, I shall address the second condition that limits the usefulness of logic as a tool for drawing conclusions from Scripture.