What are a priori, a posteriori, and a fortiori arguments?

Answer

In philosophy, knowledge is categorized based on whether it stems from universal, logical principles or relies on specific experiences and evidence. The distinction between these categories delineates a priori and a posteriori knowledge. A priori concepts are those that can be assessed purely through logic or universal truths. On the other hand, a posteriori concepts necessitate specific observations or knowledge for evaluation. This differentiation also applies to philosophical “arguments” that are either entirely reasoned or require empirical data.

A priori translates to “from the earlier.” Knowledge is labeled a priori when it can be confirmed independently of empirical evidence, experience, or observation. Put simply, a priori knowledge is acquired solely through logical reasoning. For instance, statements like “circles are not squares” and “bachelors are unmarried” are tautologies, known to be true by definition. They are considered a priori assertions. The same principle applies to mathematical statements such as 2+2=4.

A posteriori translates to “from the latter.” Knowledge is termed a posteriori when it can only be acquired through experience or other empirical methods. In essence, a posteriori knowledge is subject to being true or false, logically speaking, and thus requires assessment through actual observations. For example, the statement “John is a bachelor” cannot be verified through pure logic; empirical facts about John must be observed to determine its truth. Similarly, the statement “I have five dollars in my pocket” is potentially true or false and can only be confirmed or refuted through empirical evidence.

It is crucial to recognize that a priori knowledge does not necessarily have to be entirely deduced through logic, at least within the context of a specific discussion. The key point under consideration simply needs to be validated or refuted through reasoning.

Alone. Once a fact or idea is considered “true,” for the sake of argument, later ideas can be evaluated entirely based on the logical outcomes of that idea. For example, if both sides of a debate agree that “John was in Kansas from March 1 through March 3” is a true statement, then the statement “John was not on the moon on March 2” would be considered true a priori, for the sake of that discussion.

Note that the second statement follows as an absolute logical necessity, given the first. This is why it can be referred to as “true a priori.” If the first statement is true, the second is verified entirely based on logic, not on any particular additional fact. This is the literal meaning of a priori: “from the earlier.” Because we have accepted the earlier statement as true, we must, logically, accept the second.

The distinction between a priori and a posteriori becomes important when trying to confirm or refute certain ideas. The initial step is usually to assess a claim for a priori confirmation—essentially, is it self-referencing or logically necessary? If so, then it is “proved” a priori as true. This does not necessarily make such knowledge useful, but it does indicate that the truth value of such a statement is not up for debate. If it is not true a priori, the next step is to determine if the statement is self-contradictory or logically impossible. If so, then it can be dismissed a priori as false.

If a statement cannot be evaluated on an a priori basis, it must be analyzed using further evidence or observations: it is a posteriori knowledge. Most claims, in most instances, require some level of empirical information for examination. If a statement has not been explicitly recognized as a priori, then it is a posteriori, and the majority of human knowledge is a posteriori.

The term a priori is more commonly used. In logic and debate, the ability to classify something as a priori knowledge is a crucial distinction. However, it is uncommon to see an idea explicitly stated.Typically labeled a posteriori. When this occurs, it is generally intended to refute a claim that the statement can be known a priori.

A much less commonly used term, a fortiori, describes something related to a priori knowledge but not precisely the same. The term a fortiori means “from the stronger,” and it pertains to arguments that aim to demonstrate a “smaller” point by referencing an already proven “larger” point. For example, if a man asserts he can afford to spend $100, we infer he can afford to spend $10. If consuming one sip of a liquid is lethal, we deduce that drinking an entire cup is also lethal. If a man can hold his breath underwater for three minutes, we assume he can hold his breath for one minute. If it is deemed a sin to punch someone, we infer that stabbing him would also be sinful.

When we argue a specific point based on some larger or broader established idea, we are employing a fortiori arguments. In everyday conversation, we frequently use expressions like “even more so” or “all the more.” This is, in general terms, an appeal to a fortiori logic, and the examples provided might all be articulated using that kind of language.

Technically speaking, a fortiori arguments are not as conclusive as truly a priori statements. In the previous examples, if the man in question had received a signed check for $100 from a friend, he might only be able to spend exactly $100. In other words, it is logically feasible that he can “afford” to spend $100, but not $10, since he has no other money. Therefore, while a fortiori arguments are reasonable, they are not logically absolute, and thus not genuinely a priori.

As with all philosophical concepts, both Scripture and Christian experience embody the concepts of a priori, a posteriori, and a fortiori knowledge. The book of Hebrews rhetorically inquires, if animal sacrifice has a certain spiritual impact, “how much more” effective is the sacrifice of Christ (Hebrews 9:13-14)? This constitutes an a fortiori argument.Jesus used an a fortiori argument when He said, “If you, then, though you are evil, know how to give good gifts to your children, how much more will your Father in heaven give good gifts to those who ask him!” «If ye then, being evil, know how to give good gifts unto your children, how much more shall your Father which is in heaven give good things to them that ask him? », (Matthew 7:11)—Jesus’ point hinges on the phrase “how much more.” Paul points out that Christianity is irrevocably tied to the idea of resurrection—if there is no resurrection, then our faith is false (1 Corinthians 15:12-19). This is an a priori statement. In contrast, Paul’s immediately following remark is that Christ is, in fact, raised from the dead «But now is Christ risen from the dead, and become the firstfruits of them that slept. », (1 Corinthians 15:20), which is an a posteriori concept. Scripture invests significant importance in evidence and fact-checking (Luke 1:1-4;2 Peter 1:16;Acts 17:11).

Christian evangelism and apologetics also involve these three ideas. Some arguments for the existence of God are a priori, based on pure logic, such as the ontological argument. Assuming the universe has a beginning, the cosmological argument becomes an a priori claim. Most conversations involving apologetics and evangelism rely primarily on a posteriori knowledge, especially those discussing the reliability of Scripture or utilizing the teleological argument. Discussions of how human justice and a need for morality echo God’s traits of love and holiness are a form of a fortiori argumentation. The same is true of comparisons showing the Bible to be factual.

, historically, and scientifically reliable: given that evidence, it “stands to reason” that claims contradicting the Bible are false, based on an a fortiori approach.

Understanding the distinction between these concepts is beneficial both in matters of pure philosophy and in our interpretation of Scripture.