Law

=== Contract law ===
{{main|Contract}}
[[File:carbolic smoke ball co.jpg|thumb|The famous Carbolic Smoke Ball advertisement to cure [[influenza]] was held to be a [[unilateral contract]].]]

Contract law concerns enforceable promises, and can be summed up in the Latin phrase ''[[pacta sunt servanda]]'' (agreements must be kept).<ref>Wehberg, ''Pacta Sunt Servanda'', 775</ref> In common law jurisdictions, three key elements to the creation of a contract are necessary: [[offer and acceptance]], [[consideration]] and the [[intention to create legal relations]]. 

Consideration indicates the fact that all parties to a contract have exchanged something of value. Some common law systems, including Australia, are moving away from the idea of consideration as a requirement. The idea of [[estoppel]] or ''culpa in contrahendo'', can be used to create obligations during pre-contractual negotiations.<ref>''[[Austotel v Franklins]]'' (1989) 16 NSWLR 582</ref>

Civil law jurisdictions treat contracts differently in a number of respects, with a more interventionist role for the state in both the formation and enforcement of contracts.{{sfn|Pargendler|2018}} Compared to common law jurisdictions, civil law systems incorporate more mandatory terms into contracts, allow greater latitude for courts to interpret and revise contract terms and impose a stronger [[Good faith (law)|duty of good faith]], but are also more likely to enforce [[penalty clause]]s and [[specific performance]] of contracts.{{sfn|Pargendler|2018}} They also do not require consideration for a contract to be binding.<ref>e.g. in Germany, [http://dejure.org/gesetze/BGB/311.html §&nbsp;311 Abs. II] {{Webarchive|url=https://web.archive.org/web/20070111212855/http://dejure.org/gesetze/BGB/311.html |date=11 January 2007 }} [[Bürgerliches Gesetzbuch|BGB]]</ref> In France, an ordinary contract is said to form simply on the basis of a "meeting of the minds" or a "concurrence of wills". [[Law of Germany|Germany]] has a special approach to contracts, which ties into property law. Their '[[abstraction principle (law)|abstraction principle]]' (''Abstraktionsprinzip'') means that the personal obligation of contract forms separately from the title of property being conferred. When contracts are invalidated for some reason (e.g. a car buyer is so drunk that he lacks legal capacity to contract)<ref>{{cite web|url=http://dejure.org/gesetze/BGB/105.html|title=§&nbsp;105 BGB Nichtigkeit der Willenserklärung|work=dejure.org|access-date=5 December 2006|archive-url=https://web.archive.org/web/20061209072433/http://dejure.org/gesetze/BGB/105.html|archive-date=9 December 2006|url-status=live}}</ref> the contractual obligation to pay can be invalidated separately from the proprietary title of the car. [[Unjust enrichment]] law, rather than contract law, is then used to restore title to the rightful owner.<ref>Smith, ''The Structure of Unjust Enrichment Law'', 1037</ref>