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Coherence vs. Consistency

Consistency​

Consistency refers to the non-contradiction of statements. A set of statements is consistent if it is logically possible for all statements to be true at the same time. In other words: consistent statements do not contradict each other.

Example of Consistency:

  • "It is raining today."
  • "I will take my umbrella with me."
  • "The streets will be wet."

These statements are consistent because they can all be true at the same time.

Example of Inconsistency:

  • "All swans are white."
  • "There is a black swan in the zoo."

These statements are inconsistent because they cannot both be true at the same time.

Coherence​

Coherence goes beyond mere non-contradiction and refers to the meaningful connection between statements. A coherent system of statements is characterized by the fact that the statements are not only non-contradictory, but are also logically connected and mutually supportive.

Example of Coherence:

  • "The streets are wet."
  • "It rained recently."
  • "The clouds in the sky are dark."

These statements are not only consistent but also coherent, as they form a cohesive picture and support each other.

Example of lack of Coherence:

  • "The streets are wet."
  • "Today is Tuesday."
  • "Elephants have long trunks."

These statements are consistent (they can all be true at the same time), but they do not form a coherent whole because they have no meaningful connection.

Differences and Importance​

The main difference between consistency and coherence can be summarized as follows:

  • Consistency is a minimal logical requirement: statements must not contradict each other.
  • Coherence is a stronger requirement: statements must not only be non-contradictory, but also form a meaningful connection.

In the practice of critical thinking, we strive for both consistency and coherence. Consistency is a necessary but not sufficient condition for a convincing argument. A truly strong argument must also be coherent, i.e., its components must be logically connected and mutually supportive.