It's about deceiving without lying, misleading, answering questions not asked, and failing to answer questions which are. It's playing the smart-arse. Making sure that nothing one says could be a springboard for criticism for what has occurred. When not ''cover-up'', which it often is, it's about ''providing cover''.

It's the adroit and practised way of verbalising with mental reservations unstressed parts of speech that negate the apparent meaning, or claimed ''misunderstanding'', of questions. It never, of course, involves a lie - in some cases perjury - even if any notion of ''the truth, the whole truth and nothing but the truth'' has been strangled into meaninglessness.

Those who practise this art are often immoderately pleased at their abilities to conceal, evade, mislead and leave a completely false impression. It's ''protecting the minister''. It is regarded as one of the highest calls of duty upon the senior public servant. Even as old bonds of fidelity and confidence between politician and public servant wither, a public servant who loses a minister is careless, and one who gets a minister into trouble is negligent. To do so by wrongly describing the facts and considerations is bad - even unprofessional. To dob the minister in by telling the truth is even worse - a form of unfaithfulness worse than (though akin to) adultery.

It's also practised, as a matter of routine, by military officers answering questions from people outside the direct chain of command. Anyone else - parliamentarians, press and public - will be told only what it is convenient for government and the services to have them know.

This week, Angus Campbell, a senior soldier who has been seconded to a largely bureaucratic position - which includes oversight over Australia's concentration camps - was accused by Steve Conroy in estimates of covering up for government. He was - at least in the sense of consciously avoiding giving any information that might embarrass the government or the military. No doubt he thought that was his duty. Perhaps it is. But there has never been and should never be a tradition that an officer - or a bureaucrat - who does it is immune from criticism, or questions about whether he, or she, is really serving the public interest by extinguishment of sunlight as a disinfectant to bad policy, bad operations and bad leadership, civil or military.

Criticism is more necessary when a national security or ''operation'' or, now, ''on-water'' excuse is used to claim immunity from scrutiny, even after needless deaths. One day, indeed, there should be a public inquiry into the antecedents and limits of the claim - originally made by government, then adopted by Campbell - that the ''on-water'' activities of border command would be fatally compromised by public (and people-smuggler) knowledge of what was being done by politicians and sailors in Australia's name.

Being unhelpful to parliamentary committees is a bipartisan sport. After all, politicians hide behind bureaucrats and officers when it suits. Likewise with hiding behind the flag, by which any criticism of military judgment or activity is counted as a betrayal of the nobility of Gallipoli, or the service ethos.

The public servant or officer who deceives to protect the present minister is probably doing it to protect the Labor one before him, and the Liberal one before that. Loyal lying is to the government of the day, the policy of the hour, the tactic of the minute. It serves, usually, no long-term purpose, no higher ideal. It is sometimes founded on a naive belief that loyalty will be returned, or that a politician you protect ''owes'' you something, or is blackmailable if ever one is in a fix.

In some departments, not least Prime Minister and Cabinet, one suspects there are informal classes about being unhelpful to parliamentary committees, even, perhaps particularly, on issues that matter not a bit. In clubs, some senior public servants quietly boast to each other about how they faced down the bowling, dispatched the odd loose ball to the boundary and never once gave a chance. Even better, of course, is if one gets a moral advantage over the inquisitors. Sometimes, a parliamentary Rumpole will express frustration and suggest that the batsman is being less than completely forthright. Great umbrage can be taken, on the Ken Henry model or, now, the David Hurley model for such an infamous suggestion.

In 2011, Senator Michael Ronaldson accused Lieutenant-General Ken Gillespie, then chief of army, of ''prevaricating'' about an awards ceremony. Strictly, Gillespie had been telling the truth, but he was also prevaricating, if only by efforts to distract. He was loyally protecting the army from its embarrassment about a broken promise to veterans. And protecting David Feeney, then at the dizzy heights of his political career as parliamentary secretary for defence, who himself showed a talent for obfuscation and misdirection that might have suggested a background in factional politics, public service or both. Feeney's statements were replete with some of the classic distractors: ''Now let me clarify this …''; ''As I comprehend it …''; ''That is my advice''; ''I am advised …''; ''If that is your suggestion, then all I can say is that that is my advice and I know nothing of it''; ''I am advised now, however, …''. And so on.

Gillespie intervened to ''help'' the minister. He explained one of many sources of confusion, if by suggesting it was the only one.

Ronaldson: I am afraid, with the greatest respect, that given the prevarication in relation to this matter … I am far more prepared to accept the views of those who refused to come … I am more prepared to accept their take on this and I am more prepared to accept the take of the journalists involved than from anything I have heard today.

Gillespie: That is for you to …

Ronaldson: I thank you for your prevarication.

Gillespie: That is your choice to make that.

It is typical of the incompetence of those staffing Bill Shorten, and of Shorten himself, that this incident was misdescribed this week as Ronaldson calling Gillespie a ''coward''. He wasn't, and Shorten had to spend several days apologising.

In 2011, there was no collective intake of breath at what Ronaldson said. Chief of the Defence Force Angus Houston was in the room but did not take public umbrage and call for a return to the day when, apparently, the word of an officer and a gentleman could always be taken as absolute writ.

Ronaldson had not been suggesting that Gillespie was a pawn of Labor. He did not really mean that Gillespie had not been telling the truth. Indeed, Gillespie was telling the truth, but the truth as he saw it completely elided anything to do with the embarrassment caused Defence by the commander in chief, and the political and media reaction to the consequences. The incident, to him, followed a confusion of two separate functions, and a worthy extra tacked on to another worthy event. But nothing he said cleared the air or made things simpler. I doubt General Gillespie would have reached the rank he did had he intended to. His level of command is much more focused on assembling the resources necessary for his service to meet the needs of the government of the day - a process for intellectual, political and administration infighting, rather than traditional military virtues.

Horatio Nelson, famously, put a telescope to his blind eye during the Battle of Copenhagen so that he could say, honestly, that he ''had not seen'' an order - conveyed by flag from his commander, Sir Hyde Parker, to withdraw his ships from the fight. A former defence chief, Admiral Chris Barrie, was once accused of doing something similar in failing to update his information about whether children were thrown overboard from a refugee boat. Barrie could hardly but be aware that both John Howard and Peter Reith, with the help of their private offices, were being accused of constructing ''I wasn't told'' alibis. Formally told by Rear Admiral Chris Ritchie that there was ''no evidence'' of children being thrown overboard, Barrie told Ritchie: ''I would not change my advice to the minister [Reith] without conclusive proof that the original advice to Reith was wrong.''

Paul Kelly, in his book The March of Patriots, observed: ''Even if Barrie was unconvinced, his obligation was clear - he should have asked Ritchie to 'resolve it once and for all and report back'. But Barrie was a CDF who did not want to be convinced the story was wrong.''

It was Barrie's fate to be remembered primarily for his provision of political cover to the government of the day, over an affair that went right to the basis of any concept of military honour. Students of the military art, and those lecturing them, now learn of this, and similar incidents, as examples of what not to do.

But the military caste has little to learn about being forthright from public servants. In estimates this week, the secretary of the Attorney-General's Department, Roger Wilkins, was asked about subpoenas from the Hanger royal commission for Rudd-era cabinet documents:

Wilkins: Are you asking whether we have received such a request?

Senator Joseph Ludwig: Yes.

Wilkins: No.

Senator Kim Carr: So, no documents have been handed over, as far as you are aware?

Wilkins: Not from us.

As Crikey.com.au reported, that same afternoon, an PM&C officer told another committee a folder of cabinet documents had been given to A-G's department which, with the Australian Government Solicitor, was co-ordinating compliance with royal commission requests. Wilkins sent a letter ''clarifying'' his evidence - in language that may well have been in German. He was later asked about it.

Ludwig: Senator Kim Carr asked whether or not any documents had been handed over to the royal commission. My recollection is that your evidence was, 'Not from us' …

Wilkins: That is exactly what I did not say. I said they are not our documents.

George Brandis: In fairness, I think Mr Wilkins was being asked about Attorney-General's Department documents and his answer was strictly correct. But in order to clarify that answer - not to derogate from it but to clarify it and expand a little on it - Mr Wilkins has been good enough to provide this letter.

Ludwig: When you say, 'Not from us', there would have been documents in the Attorney-General's portfolio that related to the home insulation program, would there not?

Wilkins: No, they were not - that is my point.

Very clever, Roger Mr Wilkins. But anyone reading could be excused for resolving never to believe you on anything unless it had been parsed by Fowler, translated back and forth from German, and run up the flag and saluted by Angus Campbell.