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A Posteriori Knowledge Definition

The opposite of a priori. A posteriori knowledge is established from the research after it has been conducted.

What is a posteriori knowledge?

• Definition: Knowledge that depends on experience, observation, or evidence (e.g., scientific findings, history, sensory perception).

• Benefit: It tells you about the actual world – how things really are, not just how they must be.

  • Example: Water boils at 100°C at sea level – we only know this from testing, not from pure reasoning.

• Usefulness: Grounds your reasoning in reality and corrects false assumptions.

What is a priori knowledge?

• Definition: Knowledge you can justify independently of experience (e.g., math, logic, definitions).

• Benefit: It gives you certainty and universality. If you know something a priori, you don’t need to run experiments or collect data – it’s valid in all cases.

  • Example: 2 + 2 = 4 doesn’t depend on testing apples or coins; it’s true by reason alone.

• Usefulness: Helps you build frameworks, models or rules that don’t depend on the messy variability of real-world observations.

Why does it matter to distinguish them?

• Knowing whether something is a priori or a posteriori helps you evaluate how secure your knowledge is.

• A priori → gives strong certainty, but limited scope (applies to concepts, logic, math).

• A posteriori → gives real-world accuracy, but is always open to revision with new evidence.

• In practice, philosophy, science, and law often weave the two together: a priori reasoning frames hypotheses or principles, while a posteriori evidence tests and refines them.

In short: a priori = necessary, universal truths (independent of experience). A posteriori = contingent, empirical truths (discovered through experience).