THEORY Fourth Estate, Public Sphere defined

TBC
Basic stuff, but useful - and indeed fundamental.

IN A NUTSHELL:
With clergy/religious institutions, nobility and 'commoners' the classic 'three estates of the realm', the media (originally the press of course) began being referred to as a fourth estate, independent from and tasked with ensuring a proper scrutiny (and flow of information to and on behalf of the public) of the three estates. Edmund Burke is widely credited with coining the term in 1787 during a debate in the House of Commons ... on the commencement of press reporting on parliament.
Here's Hearns-Branaman's (2011) summary:

The Fourth Estate encapsulates many of the important ideas of the Enlightenment,especially that democracies need to be fuelled by a well informed public whothemselves are the source for the power and legitimacy of the government.

The concept of a public sphere is linked to this; the German philosopher Jurgen Habermas used it to describe the development of a class-based, fluid space for debate on and scrutiny of ideas and the pursuits and policies of the more powerful, established three estates. He sees this as linked to literacy and the rise of a pluralistic press; much like Curran and Seaton, he views the mid-1800s marketisation and corporatisation of the press industry, now largely controlled by and itself big business, as marking a decline of the concept, not the beginning of this:

Habermas, implacable opponent of postmodernist theorizing, argues that in eighteenth century England there was the emergence of a 'public sphere ... which mediates between society and state', in which 'the public organises itself as the bearer of public opinion' (Habermas (1989)). [FRRI] 

SOME RESOURCES I'VE USED:
The Wiki is a decent one.
Curran and Seaton's classic work is one of many that include detailed overviews of both concepts.
Hearns=Branaman (2011) focussed his PhD thesis on the topic, questioning the rationalism that lies at the heart of the concept. Its downloadable as a PDF.

This FRRI blog piece embeds a 2008 analysis from a reputed academic source (now offline), and scrutinises Habermas' concept of the public sphere in some detail.

'Rose's blog' (a practicing journalist):

To me the theory of a Fourth Estate is an ideal, not that journalists shouldn’t try to live out this role, but in reality it may be considered that journalists have too many constraints and influences for the ideal to be completely practicable, for example legal constraints, market forces, and ownership. In this essay will look at some of these ideas and how they affect the idea of the Fourth Estate.

The Drum - a survey into Aussie views finds that our views on media accuracy/bias are contingent on our political views and which media we're referring to. RELEVANCE? - It has been widely noted that there has been a decline in reading/exposure to views opposing those we already hold, not a great recipe for democracy or a public sphere.

ISSUES SUMMED UP:
FOURTH ESTATE AND OWNERSHIP:
Pick up a book on the press by a Media academic and you're likely to encounter one key point over and over again: the corporate ownership, and big business, conglomerate status of much of our press, is incompatible with the fourth estate notion. How can the press be separate, independent from and provide cool, neutral, rational information on a business world and political sphere it is very much a part of?
This analysis is often informed by Marxist thinking, Curran and Seaton being one example.
The wider approach is part of what is termed the 'political economy' approach to Media Studies, with Noam Chomsky the best known of these.
Curran and Seaton wrote of how they felt the 'free market' reforms, such as the scrapping of stamp duty in 1851, actually created a less free press than before, not the free press that continues to be acclaimed, from 1985's Peacock Report to the Leveson Report two decades on, as the basis of press freedom and pluralism.
When the 1960s Times sought to get rid of working class readers advertisers refused to pay for, when Murdoch shut the advertiser-boycotted NoTW to prevent wider contagion, when the Telegraph allegedly censored coverage of HSBC's law-breaking to safeguard valuable ads, when Murdoch censored critical coverage of China to further his ambitions for expansion in China ... ownership and the scale of newspaper businesses seems indeed to be a major issue.

PUBLIC SPHERE AND PLURALISM:
The public sphere requires rational, accurate information as the basis for informed debate, as does the fourth estate concept. If three RCPs, starting in 1947, found an issue with a lack of pluralism, which has gotten more pronounced since the last one reported in 1977, can we really have an effective public sphere?
If people more and more retreat to reading exclusively views that reflect their existing views, as seems to be the case (TV is the better example, especially US: Fox News), can we really have a public sphere?
If corporate-funded think-tanks and pressure groups, often hiding their paymasters, can so easily dominate public discourse (partially by providing free news in effect for media outlets which are businesses concerned with profit before all else), can we really have a public sphere? NB: source strategies is one of Chomsky's five filters.
With the increasing range of laws, justified by either protection of children or anti-terrorism, restricting free speech, can we really have a public sphere?
If the three major political parties instead of representing a genuine range of views are all neoliberal, Thatcherite, free market parties, what does this mean for the BBC's legally-binding neutrality if its 'range of views' is taken from within this hegemonic range?

RUSBRIDGER, KENNAN, HABERMAS AND DIGITISATION:
As ever, digitisation rears its head. There are those, notably Dan Gillmor, who have evangelised the rise of what is variously termed 'We Media' or UGC as denoting a reinvigorated fourth estate, decoupled from the concerns above about ownership. Even some of those enthusiasts have gradually retreated from this technotopian view.
If technology, web 2.0 and internet in particular, were mere benign tools, it would seem inarguable that the public sphere idea has been given fresh legs. Keenan