Rawls acknowledged that a society cannot choose how to govern itself in an actual negotiation between everybody involved, but he argued that:
“... a society satisfying the principles of justice as fairness comes as close as a society can to being a voluntary scheme, for it meets the principles which free and equal persons would assent to under circumstances that are fair”.
In this book, however, Rawls's argument is accepted as expressing the need for equality of treatment and inclusiveness, as discussed below (2.5), but more is needed to make governance decisions in a real society. It is assumed here that almost everyone in a society would see some governance and public services as being necessary, but that opinions will differ about their scope (2.2).
Life in a society entirely without governance would be, in the words of Thomas Hobbes, "nasty, brutish and short". In practice each society establishes a set of power relationships for a point in time, but these never satisfy everybody and they continue to evolve. People accept the need to comply with the current arrangements even while they are negotiating to change them. This might be called a ‘contractarian’ belief in the value for a society of defining and complying with an agreed form of governance, following in a tradition from Thomas Hobbes onwards. David Gauthier summarised the underlying rationale:
“The contractarian....supposes that is in general possible for a society, analysed as a set of institutions, practices, and relationships, to afford each person greater benefit than she could expect in a non-social 'state of nature', and that only such a society could command the willing allegiance of every rational individual.” 
The use of the word ‘contractarian’ has been avoided in this book, though, as it also has philosophical connotations of searching for universal principles and perfect institutions rather than the process of reaching practical agreements as described here. A similar problem applies to the word ‘contractualism’, which also seeks a philosophical justification of moral principles. The words used in this book are ‘acceptable’ and ‘negotiated’.
© PatternsofPower.org, 2014
 Rawls described "The Main Idea of the Theory of Justice" in section 3 of his book A Theory of Justice. He argued that fairness would be conducive to acceptability on p. 13 (p. 12 PDF), and he proposed the following principles:
“the first requires equality in the assignment of basic rights and duties, while the second holds that social and economic inequalities, for example inequalities of wealth and authority, are just only if they result in compensating benefits for everyone, and in particular for the least advantaged members of society”. (p. 14, p. 13 PDF)
A PDF copy of the book was available in April 2014 at http://economia.uniandes.edu.co/content/download/41151/360980/file/Rawls99.pdf.
 Thomas Hobbes’s book Leviathan was available in April 2014 at http://oregonstate.edu/instruct/phl302/texts/hobbes/leviathan-contents.html. In chapter 13 (p. 186), Hobbes described life without governance:
“Hereby it is manifest that during the time men live without a common power to keep them all in awe, they are in that condition which is called war; and such a war as is of every man against every man. …
Whatsoever therefore is consequent to a time of war, where every man is enemy to every man, the same consequent to the time wherein men live without other security than what their own strength and their own invention shall furnish them withal. In such condition there is no place for industry, because the fruit thereof is uncertain: and consequently no culture of the earth; no navigation, nor use of the commodities that may be imported by sea; no commodious building; no instruments of moving and removing such things as require much force; no knowledge of the face of the earth; no account of time; no arts; no letters; no society; and which is worst of all, continual fear, and danger of violent death; and the life of man, solitary, poor, nasty, brutish, and short.”
 David Gauthier referred to a contractarian's belief in the benefits of co-operation in his book Morals by Agreement (chapter 1, section 3.1). The text of Chapter 1 was available in April 2014 at http://philosophyfaculty.ucsd.edu/faculty/rarneson/Courses/GauthierChapter1.pdf
 The concepts described in this book may be seen as an adaptation of what is nowadays termed 'political contractarianism' – as described, for example, in The Stanford Encyclopedia of Philosophy (Fall 2008 Edition), Edward N. Zalta (ed.):
"'Contractarianism' names both a political theory of the legitimacy of political authority and a moral theory about the origin or legitimate content of moral norms. The political theory of authority claims that legitimate authority of government must derive from the consent of the governed, where the form and content of this consent derives from the idea of contract or mutual agreement."
This article was available in April 2014 at http://plato.stanford.edu/archives/fall2008/entries/contractarianism/; it was written by Ann Cudd. It traces the lineage of political contractarianism to Thomas Hobbes who, in Leviathan, Chapter 17, described a social contract that consisted of:
“a covenant of every man with every man, in such manner as if every man should say to every man: I authorise and give up my right of governing myself to this man, or to this assembly of men, on this condition; that thou give up, thy right to him, and authorise all his actions in like manner” to enable government to provide “peace at home, and mutual aid against their enemies abroad”.
The important aspect of Hobbes's concept, for this book, is the idea of reaching agreement to live in peace. His ideas on what a good government might look like are less relevant here – his preference for monarchy reflected the circumstances when he was writing, at the end of the 17th century.
The reason for avoiding use of the term ‘contractarianism’ in the main text is that it is often defined as being based upon “an ideal contract” – as is the case in Flew and Priest’s A Dictionary of Philosophy, and by Amartya Sen in The Idea of Justice where he associates it with “transcendental institutionalism”, which he defines as “searching for perfection”. Sen rejects “transcendental institutionalism” and associates himself with
“a number of other Enlightenment theorists [who] took a variety of comparative approaches that were concerned with social realisations (resulting from actual institutions, actual behaviour and other influences).” (p. 7)
In this book the focus is also on existing societies, which invariably fail to achieve “an ideal contract” or “transcendental institutionalism”, so it accords with the pragmatism of Sen’s thinking.
 Contractualism is described by Elizabeth Ashford and Tim Mulgan in the "Contractualism" entry in The Stanford Encyclopedia of Philosophy (Winter 2009 Edition), Edward N. Zalta (ed.). They quote T.M. Scanlon’s book What We Owe to Each Other:
“An act is wrong if its performance under the circumstances would be disallowed by any set of principles for the general regulation of behaviour that no one could reasonably reject as a basis for informed, unforced, general agreement.” (p. 153)
This entry was available in April 2014 at http://plato.stanford.edu/archives/win2009/entries/contractualism/.