Today there is widespread indifference to, even downright hostility towards logic and the fundamental laws that govern it. We are sometimes told that logic is a Western construction invented by DWEMâ€™s (Dead White European Males such as Aristotle), that in a postmodern world, story and narrative have replaced a cold-hearted, logical approach to life, and that Jesus was a prophet for the common man, not a logician for the â€œwise and intelligent.â€
I could not disagree more. Logic comes from the very nature of God Himself, its employment need not be cold and impersonal, it can be expressed through story and narrative as C. S. Lewisâ€™s works of fiction nicely illustrate, and Jesus used logic with â€œthe common manâ€ every bit as much as he did with the â€œwise and intelligent.â€ In what follows, I shall unpack these assertions by doing two things: present a primer on logic and God, and explain and illustrate Jesusâ€™ skill in using logic.
A Primer on God and Logic
(1) The universal validity of the laws of logic: These fundamental laws are true principles governing reality and thought, and are assumed by scripture. As noted above, some claim they are arbitrary Western constructions, but this is false. The basic laws of logic govern all of reality and thought and are known to be true for at least two reasons: (1) They are intuitively obvious and self-evident. Once one understands a basic law of logic (see below) one can simply see that it is true. (2) Those who deny them use these principles in their denial, demonstrating that those laws are unavoidable and it is self-refuting to deny them. I will support and illustrate this claim below when we look at the three fundamental laws of logic.
(2) God and the laws of logic: The basic laws of logic are neither arbitrary inventions of God nor principles that exist completely outside Godâ€™s being. Obviously, the laws of logic are not like the laws of nature. God may violate the latter (say, suspend gravity), but He cannot violate the former. Those laws are rooted in Godâ€™s own nature and govern His own mind. Indeed, some scholars think that the passage â€œIn the beginning was the Word (logos)â€ (Jn 1:1) is accurately translated â€œIn the beginning was Logic (a divine, rational mind)â€. For example, even God cannot exist and not exist at the same time; He cannot both love and hate Jesus Christ; there cannot be one God, no God and many Gods. And even God cannot validly believe that red is a color and red is not a color or that 2+2=73. Divine omniscience is defined as the idea that for all truths, God knows and believes each one, and for all falsehoods, God knows each is false and does not believe it.
When someone correctly says that God need not behave â€œlogicallyâ€ they are using the term in a loose sense to mean â€œthe sensible thing from my point of view.â€ Often, God does not act in ways that people understand or judge to be what they would do in the circumstances. But God never behaves illogically in the proper sense. He does not violate in his being or thought the fundamental laws of logic.
(3) The three â€œlaws of thoughtâ€: There are three fundamental laws of logic. Suppose P is any indicative sentence, say, â€œIt is raining.â€
The law of identity: P is P.
The law of non-contradiction: P is not non-P.
The law of excluded middle: Either P or non-P.
The law of identity says that if a statement such as â€œIt is rainingâ€ is true then the statement is true. More generally, it says that the statement P is the same thing as itself and is different from everything else. Applied to all of reality, the law of identity says that everything is itself and not something else.
The law of non-contradiction says that a statement such as â€œIt is rainingâ€ cannot be both true and false in the same sense. Of course it could be raining in Missouri and not raining in Arizona, but the principle says that it cannot be raining and not raining at the same time in the same place.
The law of excluded middle says that a statement such as â€œIt is rainingâ€ is either true or false. There is no other alternative. Letâ€™s apply our understanding of these laws of logic to the issue of their unavoidability (even for those who deny them) and the self-refuting nature of their rejection. For example, consider someone who says, â€The laws of logic are arbitrary imperialistic Western constructions that should be rejected.â€ For ease of exposition, letâ€™s call this statement â€œP.â€ If someone asserts P, they assert P and not some other assertion, say Q. And they want their listeners/readers to grasp P as their assertion. Otherwise, why would they take the time to assert P?
While lecturing at Miami of Ohio, a student actually asserted P to me and I responded by threatening to call the campus police on her because she was an animal torturer. With disbelief on her face, she asked where I got that idea. I said that since on her view, P is not P, then her P (â€œlogic is arbitrary and should be rejectedâ€) was actually Q (not P) to me (â€œthis woman tortures animalsâ€). Her assertion was, well, her assertion! And it was not â€œP and non-P (i.e., Q)â€ at the same time! And her statement was either true or false (she clearly meant for it to be taken as true) but not both. This would have become evident if I had responded, â€œGood. Iâ€™m glad to see that you think it is false that logic is arbitrary and should be rejected (i.e., non-P)!
Jesus the Logician
In his masterful article â€œJesus as Logician,â€ Dallas Willard correctly notes that while Jesus did not teach a theory of logic or explicitly call attention to logical forms, his skill as a logician resides in his accurate, powerful and precise use of logic in his teaching and debates. To see this, letâ€™s look at some examples.
Consider Matthew 22:23-33 where the Sadducees raise a reductio ad absurdum argument against Jesus. In such an argument you grant your opponentâ€™s premise, show that it leads to an absurd conclusion, and argue, therefore, that the granted premise should be denied. The argument is also an example of a dilemma syllogism (see below): Formally, the Sadducees argue thusly: If P (there is life after death), then either Q (adultery is permissible in the afterlife) or R (polygamy is permissible in the afterlife). Not-Q (adultery is not permissible, period) and not-R (polygamy is not permissible, period). Therefore, not-P (there is no life after death).
Grasping the heart of this syllogism, Jesus skillfully notes that the either/or dilemma his opponents have placed on him (either adultery or polygamy is permissible in the afterlife) both make an assumption: There is marriage in the afterlife. They argue: If there is marriage in the afterlife, then either there is adultery or polygamy. Jesus denies that there is marriage in the afterlife (Matthew 22:39), and in one simple step, he undermines the dilemma (either adultery or polygamy) they have raised against life after death.
In Mark 11:27-33, Jesus himself uses a dilemma syllogism. Put formally, such a syllogism goes like this: (1) (If P then Q) and (if R the S), and (2) either P or R, then (3) either Q or S. In context, the religious leaders are challenging Jesusâ€™ authority, and he asks, â€œWas the baptism of John from heaven or from men?â€ His argument is this: (1) (If Johnâ€™s baptism is from heaven, then the critics ought to believe Johnâ€™s teaching about Jesus) and (If Johnâ€™s baptism is from men, then the critics are in danger from the people). (2) Either Johnâ€™s baptism is from heaven or from men. Then, (3) the critics should either believe Johnâ€™s teaching or place themselves in danger from the people. Realizing that Jesus had successfully placed them on the horns of a nasty dilemma, they responded by saying â€œWe donâ€™t know from where Johnâ€™s baptism came.â€
To my mind, Jesus was the greatest thinker who ever lived. And while he did not come to develop a theory about logic or to teach logic as a field of study, it is clear that he was adept at employing logical forms and laws in his thinking and reasoning. We who are his followers should go and do likewise.