Is truth relevant any longer? Journalists are encouraged to accept the philosophy behind the adage famously coined by the Guardian’s CP Scott: comment is free, but facts are sacred.

So editors train trainee reporters to “get the facts” (and student journalists are similarly urged to do the same by their tutors).

Junior journalists soon learn that “the facts” need assembling into some kind of order and that the process can be complicated. How facts are presented has an importance too.

Stories - and that loaded description is itself revealing - are not simple constructions. They involve placing facts in some kind of order and, crucially, omitting some altogether.

Even experienced journalists, reporters and subeditors, affect to think that a collection of facts adds up to some kind of truth.

And it is widely accepted in our trade that truth-telling is the point of the job. Providing the public with the necessary “information” on which to base their views enables them to make political, economic and social decisions.

Anyone reading newspapers each day or watching TV news or listening to radio bulletins - and especially if doing all three - will know that truth turns out to be a moving target.

“The facts” suddenly dissolve. They become little more than propaganda tools as journalists twist them to suit narratives that we realise make a nonsense of the mission to inform.

This process, sometimes reduced to a supposed division between objectivity and subjectivity, has a long history. The newspapers of the 19th and 20th centuries were no more “factual” than those published today. Sacrilegious opinions always dominated the facts.

Nor should we overlook the one-sidedness of this matter. No reader, viewer and listener - no member of the public - is a blank page. Everyone who consumes the news does so with their views and attendant assumptions in place, and they are difficult to dislodge.

For some reason, clearly influenced by undue optimism, it was supposed that the creation of social media would change everything. Mainstream media’s spin would be exposed for what it is.

By contrast, unmediated media would allow the people to enjoy unvarnished facts, thus allowing “the truth” to emerge at last.

Ha! Bah humbug! Practice has made nonsense of the theory. The output on social media is not only less fact-free than that purveyed by the hated MSM, it is overly dominated by opinions.

The Guardian’s leading article today pointed out that we are living in “what some call the post-factual or post-truth political era” in which “what you would like to believe always trumps the facts.”

I agree but only up to a point because I take issue with the belief that it is a new phenomenon, a new age. Surely it has always been the case. When Scott wrote his facts-are-sacred essay in 1921, he was already rowing against the tide.

Less than a decade before, the opinions of the British people had been moulded - against their prior wishes - to accept the necessity of going to war.

And, as Scott knew well enough at one point in the war, sacred facts confided by a journalist to the prime minister, David Lloyd George, about the horrors of the frontline were kept from the public in order to prevent a peace movement gaining hold.

That is not to say that Scott’s intentions were not honourable. Nor is it to say that we should simply accept the situation and dispense with fact-hunting altogether.

But it is hugely important to highlight the fact, yes the fact, that opinions continue to hold sway in all news output. That, of course, is the major role of media commentators: to make transparent to as wide an audience as possible, as often as possible, the underlying messages of so-called facts.

I write this in the knowledge that it is a self-serving, self-justifying statement. However, I do so because it concerns me that too few mainstream media outlets now cover the media.

This is especially worrying at a time when opinions overshadow facts and at a time of media transition. Facts, as that Guardian editorial said, “need to be tested”.

Not only that. Given that contested facts - factoids, perhaps? - influence those opinions, it is crucial to provide a running analysis of what lies behind the news.

I accept that plenty of non-journalists use social media to do that, and good for them. Their problem is in gaining the trust of a large enough audience in order to hold the fact-twisters to account.

For the foreseeable future, that should be a major task for mainstream media. If journalism is to have any value to society then it has to analyse itself. What is at issue here is truth and trust.

Newspapers may be in their death throes, at least in print form. But we must not abandon our task because we know, do we not, the answer to that question about who should guard the guards?