In Westminster Parliaments, a reasoned amendment is an amendment to the wording of the motion on the reading of a bill, which turns the motion from one progressing the bill into one rejecting it.
[1][2] Consider the second reading in the House of Commons of the United Kingdom of a bill which has 200 supporters and 300 opponents.
For instance, in 1998 the House of Lords passed the following reasoned amendment:[3] Leave out all the words after "That" and insert "this House declines to give the European Parliamentary Elections Bill a Second Reading on the grounds that it includes an undemocratic 'closed list' system providing for the selection of MEPs by party choice, an approach which would end the historic right of the British people to choose the candidates they wish to be elected, a step for which the House notes with great concern no mandate was sought or given at the last general election".In this case, the Commons invoked the Parliament Acts 1911 and 1949 to override the Lords' rejection of the bill, which later became law as the European Parliamentary Elections Act 1999.
This type of amendment, which has now fallen into disuse, is a legal fiction and is deemed by Erskine May: Parliamentary Practice[5] as equivalent to a motion not granting the Bill a second reading at all.
In 1999 Gildas Molgat said "Nowadays, it is more often used to prolong debate since it allows those who have already spoken on the main motion an opportunity to speak again".