Is there an idiom or a single word for 'presumed truth'?

In his comprehensive interview at the annual Market Research Conference this year, Ian Hislop, editor of Private Eye, said of Boris Johnson, the UK Foreign Secretary, that he had given out massively incorrect details of trade figures with Korea during a speech.

Private Eye corrected the statement publicly, whereupon Boris Johnson repeated his error soon after, on radio. Ian Hislop said that this kind of thing was becoming increasingly common in politics - the habit of giving out supposed 'facts' without any sincerity at all, and without any semblance of responsibility.

Is there an idiom, or a single word, that expresses the capacity to make information public without caring whether it is true or not - but only caring about the desired consequence of the statement being made ?

It is not, exactly, 'obfuscation' - the first word that came to my mind. Nor is it, exactly, lying or deceiving if there is an underlying capacity for complete unreality. 'I want it to be true, therefore it is true' as it were. This is my truth, therefore it is truth.

It is a kind of make-believe that - making the assumption we live in a world of 'post-truth' - wishes to perpetuate itself, a desire to make the world what one wishes it to be by telling the world it is something that it is not.

Is this concept already expressed in idiom or in a single word ?

A word that covers someone making a statement for the effect, without regard to the validity :

I believe that disingenuous covers the use case you suggest.

(adj) Not candid or sincere, typically by pretending that one knows less about something than one really does.

(Oxford)

or similarly:

(of a person or their behaviour) slightly dishonest, or not speaking the complete truth:

It was disingenuous of her to claim she had no financial interest in the case.

(Cambridge)

I believe this covers your intended usage; whereby someone speaks something knowingly false or partially correct for ulterior motives.

Whether it covers the case of unintentional ignorance of the 'real' facts (if that's not a tautology) is up for debate- I'd say that making a factual assertion without knowing if it is true is disingenuous.

Phrase / Idiom

You may be interested in two phrases, if you aren't already aware of them:

• "economical with the truth", which dates back to the eighteenth century, although it because famous during the Spycatcher trial:

  Q: So that letter contains a lie, does it not?

  A: It contains a misleading impression in that respect.

  Q: Which you knew to be misleading at the time you made it?

  A: Of course.

  Q: So it contains a lie?

  A: It is a misleading impression, it does not contain a lie, I don't think.

  Q: What is the difference between a misleading impression and a lie?

  A: You are as good at English as I am.

  Q: I am just trying to understand.

  A: A lie is a straight untruth.

  Q: What is a misleading impression – a sort of bent untruth?

  A: As one person said, it is perhaps being economical with the truth.

• "terminological inexactitude", as coined by Winston Churchill:

  The conditions of the Transvaal ordinance ... cannot in the opinion of His Majesty's Government be classified as slavery; at least, that word in its full sense could not be applied without a risk of terminological inexactitude.

Both of these are wonderful British political idioms in the spirit of Yes, Minister and similar; I could see Ian Hislop using them to describe the situation himself.

'Presumed truth' may itself be an oxymoron, given that it almost implies that what is being talked about is not true. It is a slippery idea and has many nuances intention, coercion, competence, perspective, bias, and logic.

Depends on what is knowable about the world and knowable about people's internal motivations.

• truth (n)/true (adj) vs falsehood (n)/false (adj) - separate from any consideration of a sentient being thinking these things there is true and false, is a statement in accord with reality.

• lies/lying - a lie is a false statement uttered by someone intentionally. That is, the utterer knows the statement is false and wants others to think it is true. The other person doesn't know what the reality is and so must trust the utterer.

But truth itself, while not exactly slippery, is large and fuzzy, there are many aspects of it and sometimes things are vague and sometimes depends on context.

• misleading (adj) - a motivated speaker can utter a truth, something that accords with reality, but it is such a small irrelevant case, or takes advantage of unspoken very biased assumptions, that it metaphorically points in one way when the general truth is in the other. Something that is misleading is spoken in order that it is not false; it may literally be the case, but in almost all instantiations as intended really doesn't hold.

• white lie is a lie told to hide an unpleasant truth. It can be an outright lie "Doctor, will I survive the head transplant surgery?" "You'll be fine", or it could be just misleading "You have double the chance of the last guy". It is well-intentioned, used to reduce upset in the listener rather than for the benefit of the speaker.

• bullshit (bombast) (n) is a statement that may or may not be true and the utterer doesn't care or doesn't know what the truth is behind the statement. The utterer may be intentionally trying to mislead and just doesn't know what the truth is, or believes deeply but without any way of possibly knowing. Sometimes this word is used for 'lying' when it is not known what the utterer's internal state is (or may be a euphemism for lying). 'On Bullshit' is a short and entertaining monograph by Harry Frankfurt that discusses the complicated truth status of the term 'bullshit'

Of course there are all sorts of turns of phrases that one can create on the fly to describe various political situations, all of them used or abused or misused in the ways that the other phrases may describe.

There is a quote by Schopenhauer, who quotes Goethe from Faust, that is cynical about the whole thing (in English):

Schopenhauer, The Art of Being Right

You may also puzzle and bewilder your opponent by mere bombast because:

Usually people believe that if they only hear words, that there must be some meaning in them.

Schopenhauer - Die Kunst, Recht zu behalten, Kunstgriff 36

Den Gegner durch sinnlosen Wortschwall verdutzen, verblüffen. Es beruht darauf, daß

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