“... the nasty fact is that our winner-take-all election system, adopted from 18th century England, has the potential to leave up to 49.9% of the voters in any district feeling unrepresented -- whatever their race or ethnicity.”    USA Today editorial, 6/30/95

"The system of proportional representation ensures that virtually every constituency in the country will have a hearing in the national and provincial legislatures."                    Bishop Desmond Tutu, The Rainbow People of God, 1994

"The case for [P.R.] is fundamentally the same as that for representative democracy. Only if an assembly represents the full diversity of opinion within a nation can its decisions be regarded as the decisions of the nation itself."     Encyclopaedia Britannica

“Geography has, however, become less relevant to political identity, despite the role of federal political structures in sustaining differences based on it. It was largely supplanted early in the century by the strong party identification that became characteristic of Australian politics.”                          Marian Sawer, Dilemmas of Representation, Australian National University

"Because of our peculiar electoral law, the American government is divided between two parties.  The American people are not."   Michael Lind,  Atlantic Monthly, August, 1992

In a nutshell

In both the 1998 and 2001 Australian federal elections for the more influential House of Representatives, the majority of voters ended up with a representative who was not their first choice on the ballot paper. In a country that prides itself on being a democracy, the average voter was not represented by the candidate he or she specifically wanted. Countries with similar Single Member Voting (S.M.V.) systems such as the United States, Canada, India and Great Britain experience situations of political representation that are not that different. The reporting of any candidate who “won a hard fought battle” or “just manages to defeat his opponent” simply means that approximately half of the voters in that region are losers, stuck with a representative they do not want.
Voting turnout is significantly higher in democracies which practice proportional representation, for the very simple reason that citizens have a greater motivation to be involved in the decision making process when their choice can be from more than just two viable alternatives. The dichotomy of what is often described as the “dweedle dee, dweedle dum” option of either the government or the official opposition, leads many to believe that voting will  unfortunately solve little.
In the twenty first century most democracies now practice proportional representation, leaving ironically the so called bastions or citadels of democracy, Britain and the United States, as well as others, stuck with anachronistic systems unsuitable for the modern multicultural world, where only two viewpoints can allegedly represent everyone.
Proportional representation is the ideal system for all legislative houses, not only from the practical considerations of being able to eradicate the problems of gerrymandering and malapportionment, as well as minimising the practice known as pork barrelling, but also from abiding to the basic tenet of liberal democracy: majorities may rule, but all of the people should be represented.

What Proportional Representation is

Proportional representation is a voting system whereby successful parties gain seats in a country’s legislature (Congress, Parliament, Bundestag, Knesset, Diet, Chamber of Deputies, etcetera) in direct proportion to the number of votes they accrue at an election. -- One might ask how it could be any other way.
Centuries ago at the time the concept of the people themselves electing their leaders was barely developing, the technology of communications was at a nascent stage which tended to make elections local in character. Apart from the impracticality of voting for someone residing at the other end of the country, it was assumed that people would vote for only someone they knew or could address, in their own locality. Thus the country was divided up into a large number of electorates of approximate equal population, each electing one representative to send to the nations legislature. This single-member-voting system that developed is the antithesis of proportional representation (see below).
From the very beginning the problem rose that as each candidate does not win by the same margin, and as minority viewpoint parties might contest every electorate and still win no seats, the resulting composition of winning parties is often far from accurately representing the viewpoints of the voting public.

Why must the criterion of representation be fixed?

Throughout the world there are two basic types of electoral systems practiced by democracies:  geographical criterion representation and indeterminate criterion representation.

Geographical Criterion Representation (a.k.a. single member, pluralist, first-past-the-post, or majoritarian voting)

1. For an election, the country is divided up into a large number of  electorates /districts /constituencies /divisions. Political parties and independents will contest each one of these in a discrete mini-election to determine which one person is to represent the area in the national legislature.  Every candidate has to attempt to convince the majority of the constituents of their area that he would be their best representative. He has to be ‘all things to all men’.
2. You, as a resident of that electorate are defined by where you live. Your member (congressperson / member of parliament) represents not so much a political party but all residents of that electorate.
3. The member is identified in the legislature as, for example, the “member for Melbourne Ports”, “representative of the 24^th district”.
4. The member is answerable to the residents for all their concerns about government (at least to the degree that he can represent all the divergent interests at the same time).

Indeterminate Criterion Representation (a.k.a. proportional representation)

1. There are no mini-elections but just one whole election where all the votes are brought together to be tallied. A winning candidate may have accrued his votes from any or all parts of the country. Parties and independent candidates design their agenda / political platform according to what they see as the important issues of the day, and then offer themselves to various segments of the voting public. They are successful to the degree that they are viewed by sections of the public as responsible and accommodating to the voter’s specific concerns.
2. You, as a voter, are defined by what you want to be defined by. Your representative in government represents your chosen interests.
3. The member is identified and easily labelled as, for example, the Greens parliamentarian, the Republican, the Democrat, the Christian Socialist, the Libertarian, the Free Trader, the parliamentarian for the wheat growing district, the parliamentarian for the inner cities, the parliamentarian for the diary district, the parliamentarian representing pensioners, the gay rights parliamentarian, the parliamentarian representing the indigenous.
4. The member is answerable to those who voted for him in that he is answerable to his or his party’s declared platform.

The perennial problems associated with geographical criterion representation is that, with regards to political decision making, it is taken for granted that voters should be defined by where they live. There is the assumption that a person only looks at the important issues of the day from the perspective of someone who lives in his geographical area. We are asked to believe that a person walking into a polling booth will ask : “Which of the candidates on offer is going to be the greater benefit to the residents of my area of town?” Is it not possible that he might be more concerned about those of his own economic status, religion, profession or beliefs and values?
This site suggests that voters should have the autonomous right to define themselves by any criterion they choose, including: position on social / human rights issues, economic status, occupation type, age, gender, religion, as well as geographical region.
To divide the state up into electoral zones for the sake of the ‘local concerns of the voters’ would appear to be merely an excuse to raise the necessary quota for wining a seat so as to deny unwelcome minorities the opportunity for political representation.

The problem of proportional representation and unstable governments

One of the most common arguments against the implementation of proportional representation as a vehicle to elect parliamentarians is that, in often creating a legislature with multiple political parties, a stable coalition representing a majority to form government cannot always be counted upon. The most often example used to support this argument is that of the turbulent history of the government of post-war Italy wherein changes of government happened on an almost annual basis. Another is that of New Zealand where after a recent election Prime Minister Helen Clark, in order to garner a majority, had to accept an offer of support from the leader of a small party on the extraordinary condition that he become what is termed ‘the Minister of Foreign Affairs outside cabinet’, that is, a minister who is not bound by the concept of cabinet collective responsibility.
‘Responsible’ Government
The potential for this government instability arises in countries with so called responsible governments, governments where the executive is both appointed and removed by, and thus responsible to, the legislature. Under this system the office of the prime minister (or the president or chancellor) is awarded to the leader of any party in the lower house which manages to control a majority of the seats either on its own or in coalition with one or more other parties. 
Even though there have been many examples of responsible governments that were both elected by proportional representation and also managed a history of stability (Germany, Israel and South Africa would be three), the criticism is valid to the degree that instability can occur. However it is not valid in that it is a condemnation of proportional representation.

Separation of Powers

“Separation of powers is the division of the legislative, executive and judicial functions of government among separate and independent bodies. Such a separation, it has been argued, limits the possibility of arbitrary excesses by government, since the sanction of all three branches is required for the making, executing, and administering of laws.”          Encyclopaedia Britannica 2008 Ultimate Reference Suite

The problems in governments like that of New Zealand or Italy are not derived from their electoral systems.  Proportional representation merely acts as a catalyst to highlight the inherent flaw in the underlying set up of their governments. That is, the lack of accommodation for the classic principle of the separation of powers. In a true liberal democracy, just as there should always be a separation of legislature and the judiciary, and the executive and the judiciary, there should also be maintained a proper separation of executive and legislature. So as to prevent a conflict of interest between those who execute the law and those who make the law, both arms of government should abide by the separation of powers concept and thus be established independently of each other.

“For the constitution, rather than suggesting that all behave in a godlike manner, recognises that, to the contrary, people are swine and will take any opportunity to subvert any agreement to pursue what they consider to be their proper interests.
To that end, the constitution separates the power of the state into those three branches which are for most of us Americans (I include myself) the only thing we remember from twelve years of schooling.
The constitution, written by men with some experience of actual government, assumes that the chief executive will work to be king, the parliament will scheme to sell off the silverware and the judiciary will consider itself Olympian and do everything it can to much improve (destroy) the work of the other two branches.
So the constitution pits them against each other in the attempt not to achieve stasis but to allow for the constant corrections necessary to prevent one branch from getting too much power for too long.” playwright and screenwriter David Mamet^#

This separation is simply accomplished in all so called presidential governments as exist in countries such as France, South Korea, Indonesia, and the United States. The people vote to elect their representative in the legislature, and they also vote, on a different ballot paper, to elect their chief executive. Neither politicians have the arbitrary power to remove the other from office, and whatever the electoral system, governments, because they are directly elected for a set term, can never become unstable.

The myth of small parties winning the balance of power and “holding the government to ransom”

One of the most ridiculous arguments against proportional representation is the invention that, when no party has a majority in the legislature, a small party, in having the “balance of power” by offering to support or threatening to vote against, can control the passage of all legislation. How this allegedly works is that, when one political party in the legislature becomes the largest party, albeit with still a minority of seats, it tends to develop the imprimatur of representing most of the people and the community in general. There is then supposedly a grave injustice when a small party threatens to deny it support to get what it believes to be important legislation passed. However the fact is that if and when it can not get specific legislation passed, it is not because a small party denies it its (for example) five percent (of the vote) support, it is because all other parties deny it approximately 53% support. It is quite difficult to see why there should be any injustice when legislation can not attain passage because the majority of the people’s representatives do not support it. (see also: “Extremist Parties”)

^# David Mamet, ‘Why I Am No Longer a ‘Brain-Dead Liberal’  The Village Voice, March 11 2008.