The politician's syllogism, also known as the politician's logic or the politician's fallacy, is a logical fallacy of the form:
- We must do something
- This is something
- Therefore, we must do this.
The politician's fallacy was identified in a 1988 episode of the BBC television political sitcom Yes, Prime Minister titled "Power to the People", and has taken added life on the internet. The syllogism, invented by fictional British civil servants, has been quoted in the real British Parliament.
In Yes, Prime Minister, the term is discussed between two high-ranking civil servants who are concerned that the prime minister wants to implement a scheme to reform local government due to political opposition there. In this issue, as with many other issues humorously explored by the show, the civil servants believe that doing anything is worse than doing nothing because actions tend to undermine the dominance of the civil service. They identify the politician's logic as a fallacious categorical syllogism:
- All cats have four legs
- My dog has four legs
- Therefore, my dog is a cat.
This invalid form of argument, labeled AAA-2 among syllogisms, commits the fallacy of the undistributed middle: it says nothing about all things having four legs (the middle term) and thus the conclusion cannot logically follow from the premises, even if the premises are sound. The politician's syllogism similarly says nothing about all known "somethings" that could be done. As is common with fallacious undistributed middle arguments, it can also be seen as the fallacy of affirming the consequent when restated as an equivalent hypothetical syllogism:
- To improve things, things must change
- We are changing things
- Therefore, we are improving things.
See also 
- Chen, Raymond (26 February 2007). "The politician's fallacy and the politician's apology". The Old New Thing. Retrieved 17 April 2011.
- House of Commons (19 January 2005). Column 850: http://www.parliament.the-stationery-office.co.uk/pa/cm200405/cmhansrd/vo050119/debtext/50119-14.htm
- Joyce, George Howard (1908). Principles of Logic. Longmans. p. 205.