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

A Graduate-Level Exploration of A Priori, A Posteriori, and A Fortiori Arguments in Theology and Philosophy

In philosophical discourse, arguments are often categorized based on how knowledge is derived. This classification includes a priori, a posteriori, and a fortiori arguments, each reflecting a distinct approach to understanding truth and reality. These categories are also significant in theology, particularly in Christian apologetics and scriptural interpretation. This expanded analysis explores these concepts, their implications for Baptist theology, and their biblical applications.

1. A Priori Arguments

Definition:
The term a priori means "from the earlier" and refers to knowledge or arguments derived independently of experience. A priori reasoning relies solely on logic, self-evident truths, or universal principles. In other words, a priori arguments are those whose validity can be determined without appealing to empirical evidence or observation.

Examples in Philosophy:

• Mathematical truths, such as 2 + 2 = 4, are a priori because they do not require empirical verification.

• The statement “All bachelors are unmarried” is true by definition and is therefore an a priori truth.

Biblical Applications:
A priori reasoning often appears in Scripture, especially in logical deductions about God’s nature. For example:

• “In the beginning God created the heavens and the earth” (Genesis 1:1, NKJV). This presupposes God’s existence as the Creator, a foundational truth upon which further theological reasoning is built.

• The apostle Paul uses a priori reasoning in Romans 1:20: “For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse.” Paul argues that the existence of God is logically evident through creation, independent of direct experience.

Theological Implications:
A priori arguments are crucial in apologetics, especially when addressing foundational questions about God’s existence. For instance, the ontological argument for God’s existence, championed by Anselm, relies entirely on a priori reasoning. It argues that the concept of a “greatest conceivable being” necessarily entails the existence of God.

2. A Posteriori Arguments

Definition:
The term a posteriori means "from the latter" and refers to knowledge or arguments derived from experience, observation, or empirical evidence. A posteriori reasoning is contingent on external data and is validated through investigation.

Examples in Philosophy:

• The statement “Water boils at 100°C at sea level” is an a posteriori truth, confirmed through observation.

• Historical claims, such as “George Washington was the first U.S. President,” are a posteriori because they rely on recorded evidence.

Biblical Applications:
A posteriori reasoning is frequently used in Scripture to validate God’s work through observable events:

• The resurrection of Jesus Christ is an a posteriori claim, rooted in historical evidence and eyewitness testimony: “He was seen by Cephas, then by the twelve. After that He was seen by over five hundred brethren at once” (1 Corinthians 15:5–6, NKJV).

• Luke emphasizes empirical verification in the introduction to his Gospel: “It seemed good to me also, having had perfect understanding of all things from the very first, to write to you an orderly account, most excellent Theophilus” (Luke 1:3, NKJV).

Theological Implications:
A posteriori arguments play a central role in evidential apologetics. For example:

• The teleological argument, or the argument from design, observes the complexity and order of the universe to infer the existence of an intelligent Creator.

• Fulfilled prophecy serves as an a posteriori validation of the divine inspiration of Scripture. For instance, the prophecy in Micah 5:2 about the Messiah’s birthplace is confirmed in Matthew 2:1.

3. A Fortiori Arguments

Definition:
The term a fortiori means "from the stronger" and refers to arguments that draw conclusions about a lesser point based on a greater, already-established truth. These arguments assert that if something is true in a stronger case, it must also be true in a weaker case.

Examples in Philosophy:

• If a man can lift 200 pounds, it is reasonable to conclude he can lift 50 pounds.

• If drinking a gallon of a toxic substance is fatal, it is a fortiori true that drinking a cup of it is also fatal.

Biblical Applications:
A fortiori reasoning is explicitly used in Scripture:

• Jesus uses an a fortiori argument in Matthew 7:11: “If you then, being evil, know how to give good gifts to your children, how much more will your Father who is in heaven give good things to those who ask Him!” If earthly parents, flawed by sin, can give good gifts, then it is even more certain that God, who is perfect, will give good gifts to His children.

• The author of Hebrews employs an a fortiori argument to contrast the sacrifices of the Old Testament with the ultimate sacrifice of Christ: “For if the blood of bulls and goats and the ashes of a heifer, sprinkling the unclean, sanctifies for the purifying of the flesh, how much more shall the blood of Christ, who through the eternal Spirit offered Himself without spot to God, cleanse your conscience from dead works to serve the living God?” (Hebrews 9:13–14, NKJV).

Theological Implications:
A fortiori arguments are powerful tools in preaching and teaching, as they build on established truths to emphasize greater theological realities. They highlight the superlative nature of God’s attributes and works.

Conclusion

A priori, a posteriori, and a fortiori arguments each play vital roles in theology and apologetics. A priori reasoning establishes foundational truths about God and His nature, a posteriori reasoning appeals to empirical evidence and historical facts to affirm faith, and a fortiori reasoning emphasizes the greater certainty of spiritual truths based on already-established principles. Together, these approaches enrich our understanding of God and equip believers to effectively articulate and defend their faith:

• “Sanctify the Lord God in your hearts, and always be ready to give a defense to everyone who asks you a reason for the hope that is in you, with meekness and fear” (1 Peter 3:15, NKJV).