Problem is can anyone ever know the real truth. Often facts are facts with caveats.

As mentioned previously, a lie requires intent to deceive. If you don't know it's false there can't be an intent to deceive. Just so you're clear trump LIES continually

All truth in the end is subjective, and follows the paradigms of the questioner, their experiences and current knowledge. Thus, if one can justify a statement, then it is true and not a lie. Many NAZIs lived by the knowledge that Jews and others are lesser animals. To them, that was true, to me it is a lie.
That was fairly easy, but now consider the notion that god created man, then woman in the garden of eden. Science shows that all complex life on earth starts out as female and around 50% of humans mutate into females. Using this supportable science, then the bibles/torah/quoran has it arse about face and Eve came about first with Adam being drawn from her rib (Lilith being discarded). Yet Adam is still being preached as the first born. Ergo, a lie.
Then internal and external truths, but I'll save that for another time if people wish to keep reading.

A lie detector works on the premise that when you are making an obvious effort to distort the truth your body will generate enough signals to catch you in the act. So using that yardstick, a lie requires a deliberate departure from what you believe to be true. Absent that it is not a lie. Consider the scenario of the man with an eye condition where colors are distorted for him. Blue looks the same as green to him. When he says the sky is green or the same color as the leaves of the tree, he is not lying. That is his truth.

"History is a set of lies agreed upon.”

Napoleon Bonaparte

When you tell a lie it is because you know in your mind that you are lying. Telling an un-truth is another matter. Most of us know when we are not telling the truth. By this logic you know that when Charlie tells you he has pixies living in his shoes or that there is an invisible man watching you in the sky, Charlie is either:

1. Indoctrinated early on into his belief or decided it was true because he has always heard it is true.
   OR
2. Charlie is as crazy as a loon.

This last idea is an expression as I'm not sure loons (birds) are crazy. It may also go back to the word "lunatic" which involves asylums or the moon having something to do with ones beliefs.

If you don't know something is true and you pass it, it is a RUMOUR.... if it is not true, it makes you a liar. Don't pass rumours, they can destroy people's life and cause strife in your community. Sometimes an apology is not enough to undo what you have done. Why would you want any negativity associated with you like that?

If in doubt, I always consult the wisdom of George Costanza:

Always a good idea to not only say what it is that you believe to be true, but also your reasons for believing it to be true. The person you are talking to then has a better idea what weight to give to your certainty. If however you are not honest about why you believe something to be true, this can make it a kind of a lie, however much you believe it to be true.

Basic premise is that for something to be true you must believe it to be true and it must be true. St Augustine wrote a critical study of lyings called, of course, On Lying. Augustine might be considered the forerunner of truth tables. Four possibilities. You say it's true and it is true; You say what you believe is true and it's false; You say it's False and it is in fact False; and, you say it's False, believing it to be true. The key thing is that lies are meant to deceive; truth states are meant to illuminate reality. As Bruce asks, is a dream just a lie if it don't come true, or is it something worse?

If I knew it wasn't true then it would be a lie.

To lie is to knowingly deceive. Is there a lie hidden in the statement, I know there is a God? Maybe, I suspect that people lie to themselves all the time.

I respect your advice that people need to fact check before making a claim of truth. Or at the minimum state that what the claim they’re offering hasn’t been fact checked. It’s a practice that becomes second nature quickly. People would be surprised to discover how much we claim is incorrect.

Rationalization is an interesting form of a lie. The example of the man using the N word and claiming it is innocent is an example. That is not the same as someone making a false statement he truly believes to be true. That, I would call a mistake. Everyone has their own take on reality. As Einstein said, there is no such thing as objectivity...that pure objectivity is impossible. Therefore, pure truth is an absolute that we should all seek to obtain. Truth is a skill and a process, always striving to obtain this absolute. Every time we declare a truth, especially when it is difficult to do so, we strengthen our ability to be truthful. Every time we lie, we weaken our ability to attain truthfulness. Case in point: Trump. He lies so much that he can't be truthful. For him, that skill is gone completely.

Some of you might say science is an absolute. But science is always changing. What is proven right today is proven wrong tomorrow. Yes, there are absolutes in science, like gravity. You could say that science is an effective pursuit of Truth and science does get close. Then again, many of us confuse technology with science. Technology is the application of science..not science. Monsanto claims their technology is science, thereby silencing some who oppose their destructive activities.

If you intend to lie but mistakenly tell the truth, is it a lie? Seems to me that if/when it's immoral to tell a lie, it is equally as immoral to try to lie even though you fail to pull it off--regardless of whether you call it a lie or not.

Lie is an intentional act, or at the very least a reckless disregard for truth. Yes, we all have responsibility in attempting to ascertain the truth, but the truth can be ... elusive. I don't think ignorance equates with lying. I am not sure which is better, lying or ignorance.

Is a poison still a poison if you don't know it is a poison?

I think that is a fair analog because most poison is served up as part of an inherent lie. ... Here, eat this, its good for you!!

So, THAT explains President Don-Jon's situation perfectly! He doesn't tell lies, he just doesn't have enough sense to know what is true and what is false. Problem solved! Larry in western Kentucky

Do Bears stink if no one is around to smell em?

I think when you tell something without knowing its true, even if you think it might be true,....it comes under the heading of "gossip".

This question could raise quite a response, were it directed to Donald Trump. I would love to know what his answer would be, since it is inconceivable that he does not know that virtually everything he says is a lie, something he would never acknowledge! He could fill a chapter in the annals of Psychiatric Medicine!

I have a regular statement I make when engaging total strangers in debate: "If you want to believe lies that's your business. If you want to repeat lies it becomes my business." And somehow I've managed to avoid bodily injury (so far).

No, It's only a lie if you know it is not true.

Although intent is important to define lies or mistakes, since you are asking about responsibility in spreading lies, then I must make a clarification now that social media has become the source of so many conspiracy theories. Many people do not filter even with a modicum of common sense or logic diseminating memes or links of stupidity or conspiracy theory bullshit that doesn't pass any smell test, but then when somebody calls our gullibility for spreading shit, lots of people eash their hands saying "oh, I did it without knowing and with the best of intentions, in case it may help or warn someone." In that case, yes; I would say you are willingly spreading lies. I hate when that happens!

I Agree. Reminds me of the old telephones "party lines", politicians, G5, used car salesmen, and religion. Its endless!

Different people can have different truths. From the point of view of a committed theist, if I was to tell him that his particular god cannot exist, then he is perfectly entitled to call me mistaken as to fact, but he is not entitled to call me a liar.