Contingency (philosophy) – Status of propositions that are neither always true nor always false
defeasible reasoning – Reasoning that is rationally compelling, though not deductively valid
Deniable encryption – Encryption techniques where an adversary cannot prove that the plaintext data exists - claim that a ciphertext decrypts to a particular plaintext can be falsified by possible decryption to another potential plaintext
Fallibilism – Philosophical principle that human beings could be wrong about their beliefs, expectations, or their understanding of the world