Most people see being honest and lying as two extremes in black and white. But I think it is more accurate to conceptualize it as a spectrum with shades of grey. Being truthful is different from being correct or accurate in your statements; it is about your beliefs when you make a claim.
People are usually said to have told a lie when they make an assertion that they believe to be false. But think about it, this is too narrow of a definition since "white lies" satisfy this definition but would not be unethical because the consequences are good for everyone involved, and lying by omission where you avoid making the assertion is not a "lie" but is immoral.
A lie is not always immoral sometimes the intent behind the lie is positive. Someone might lie about a surprise party to maintain the surprise. Most pragmatic people understand since the purpose of the lie is not malicious, it is not unethical.
But who decides if the outcome is good for you? It is a slippery slope when we start justifying lies saying it is for his benefit. A boyfriend might lie about his past because he thinks it is better for her to never know, but if she ever finds out, she might feel betrayed. Was that a white lie? maybe a nobel lie? We need to be able to predict the counterfactuals accurately to be sure. Will she say "I wish you never told me", will she mean it?
So two conditions for a lie - assertion and falsehood. Let us examine the first condition. Does it have to be a strong assertion? People like scientists find it hard to make strong claims; they use qualifiers and talk about how "there is a chance that", "it seems likely", "the evidence suggests", etc. But even when people leave themselves such an out and make soft claims, if we find out they were saying something they did not believe, we still call it lying.
This is because they were misrepresenting their beliefs. The important condition is always if their words match their true internal beliefs. When people lie, they seek to manipulate and get the victim to operate based on incorrect information. They communicate in bad faith.
If someone themselves were told wrong information and then they passed it on because they believed it, then they are not "lying". They believed the falsehood to be true when they passed it on, so the intentions are clean here. They were just used as a tool by the creator of the lie to spread falsehood. It could also be a misunderstanding. But it is hard to know the internal states of humans; anyone can claim to have deceived themselves.
Misleading people is a very useful tool in the arsenal of con-men, scamsters, and tricksters. When you want to cheat or deceive people, it works better when you set up circumstances leaving clues for them to find. Discovery always beats disclosure if you want them to trust the data. It is sort of like inception, because you want the mark to think it was his idea. These criminals don't do the thinking for the victim; telling him what to believe is a very crude, blunt lie.
So lying fundamentally works by distorting the "map" used by the victim. If he believes us, we change the reality of that person; we leverage his trust to change the data he bases his decision on. But it does not have to be new incorrect data; by holding back relevant information you can do similar damage.
The legitimate way to change the behavior of a person is to communicate and change the algorithm he applies. You can also bring his attention to relevant true data, but what if you cherry-pick the data? What if you decide to not inform them of information that you know would be of use to him?
Lying by Omission
Many people try to claim they did not lie based on a technicality, "I did not say anything false, I just withheld relevant information.", "They did not ask me" these people phrase their answers in a technically true way, but it is a lie in spirit since they knew what the person was asking but chose to give them incomplete data to work with.
Often they answer ambiguously in an evasive way, trying to change the direction of the conversation. We all do this; we try to shift the topic away from uncomfortable topics. This is not lying, but it is not being honest either. This is where the shades of grey are apparent.
In fact, the famous oath used by witnesses explicitly states "the whole truth", which means withholding information is perjury.
“Do you swear to tell the truth, the whole truth, and nothing but the truth?”
But in practice, it is hard to prosecute lying by omission. When people think in black and white, using rigid categories, often some grey items like these are misclassified.
Lying by omission is one such grey area that should stay in the black region and not go to the white area, in my opinion. But I understand it has uses for the emotionally intelligent among us to make interpersonal interactions frictionless.
There are even more levels to this. The only way you can maliciously hold back the whole truth is if you have access to all the relevant facts.
Is it a form of lying to consciously avoid learning the relevant facts? You might do this when you decide in advance what you want and just search out supporting evidence. So you can honestly answer all the questions because you genuinely don't know anything more.
Say you want to quit your job, you don't look into all the possible risks, the potential issues. So when you discuss this with your wife or parents, you can honestly convince them why your idea is great. You put the onus on them to find out the potential risks.
This is why it is important that both of you share the same goals with the same priority - the long-term success and stability of your career over avoiding the short-term stress of the job. Then you will surely look for all the relevant information you need to make an informed decision.
This often is not conscious; we subconsciously avoid uncomfortable truths. We like echo chambers and don't enjoy challenging our preconceived notions. Confirmation bias affects all of us, even influencing what we remember!
The purpose of lying is not always malicious; it could be to maintain privacy. My income, weight, sexual history, etc. There are many things that people agree I have a right to hide. To effectively achieve this, I need to deploy some level of deception. I can't answer "I don't want to talk about it" in a blunt way if someone jokes about me earning less than 60k INR. That would be a dead giveaway that they are likely correct and hit a sore spot. So context is very important when we judge the morality of lying.
I see the spectrum of lying going from ethical to unethical as,
lies to protect privacy,
redirecting conversation topics,
learning in a biased way to reinforce beliefs,
lying by omission,
Ideally, we should all strive to be as honest as possible. Make sure our words and actions represent our true beliefs. This creates a high trust environment which allows for way more productivity and happiness.