What is Bad Faith?

Legal Definition
Bad faith (Latin: mala fides) is double mindedness or double heartedness in duplicity, fraud, or deception. It may involve intentional deceit of others, or self-deception.

The expression "bad faith" is associated with "double heartedness", which is also translated as "double mindedness". A bad faith belief may be formed through self-deception, being double minded, or "of two minds", which is associated with faith, belief, attitude, and loyalty. In the 1913 Webster’s Dictionary, bad faith was equated with being double hearted, "of two hearts", or "a sustained form of deception which consists in entertaining or pretending to entertain one set of feelings, and acting as if influenced by another". The concept is similar to perfidy, or being "without faith", in which deception is achieved when one side in a conflict promises to act in good faith (e.g. by raising a flag of surrender) with the intention of breaking that promise once the enemy has exposed himself. After Jean-Paul Sartre's analysis of the concepts of self-deception and bad faith, bad faith has been examined in specialized fields as it pertains to self-deception as two semi-independently acting minds within one mind, with one deceiving the other.

Some examples of bad faith include: a company representative who negotiates with union workers while having no intent of compromising; a prosecutor who argues a legal position that he knows to be false; an insurer who uses language and reasoning which are deliberately misleading in order to deny a claim.

Bad faith may be viewed in some cases to not involve deception, as in some kinds of hypochondria with actual physical manifestations. There is a question about the truth or falsity of statements made in bad faith self-deception; for example, if a hypochondriac makes a complaint about their psychosomatic condition, is it true or false?

Bad faith has been used as a term of art in diverse areas involving feminism, racial supremacism, political negotiation, insurance claims processing, intentionality, ethics, existentialism, and the law.
-- Wikipedia
Legal Definition
A term that generally describes dishonest dealing. Depending on the exact setting, bad faith may mean a dishonest belief or purpose, untrustworthy performance of duties, neglect of fair dealing standards, or a fraudulent intent.

See Good faith (contrast).
Legal Definition
The opposite of "good fnith," generally implying or involving actual or constructive fraud, or a design to mislead or deceive another, or a neglect or refusal to fulfill some duty or some contractual obligation, not prompted by an honest mistake as to one's rights or duties, but by some interested or sinister motive. Hiigenberg v. Northup, 134 Ind. 92, 33 N. E. 786; Morton v. Immigration Ass'n, 79 Ala. 617; Coleman v. Billings, 89 111. 191; Lewis v. Holmes, 109 La. 1030, 34 South. 66, 61 L. It. A. 274 ; Harris v. Harris, 70 Pa. 174; Penn Mut. L. Ins. Co. v. Trust Co., 73 Fed. 653, 19 C. C. A. 316, 38 L. R. A. 33, 70; Insurance Co. v. Edwards, 74 Ga. 230.
-- Black's Law Dictionary