From “Growing in the character of a disciple”: Chapter 10 – How we can develop ‘the love of the truth’ and the character quality , and habit, of truthfulness?
However, there can be circumstances where to leave out, or fail to mention, some fact would amount to misleading someone and in a dishonest way. That can apply even where there is no Court involved and nobody is giving evidence. Our conscience has to guide us. In any given situation we have to decide whether we can, with integrity, choose not to say something.
It is impossible to create a hard and fast rule, because every situation turns on its own facts. You must therefore ask God to guide you in those specific circumstances. Then use your conscience to gauge what is right on that occasion. The more inherently honest and sincere a person is, the more they will tend to assume that total frankness and transparency are needed. However, that is not always wise, and it can sometimes be naive to think that way, depending on the facts.
We have to ask ourselves whether the person is entitled to be told the whole truth
A good question to ask oneself, when seeking to decide how much one is obliged to disclose, is whether the other person is entitled to be told the whole truth. They may, or they may not be. If they are a police officer, judge, tax official or officer of the Court, the likelihood is they would be entitled to 100% of what you know, without leaving anything out. However, if the other person is a work colleague, friend, relative, neighbour etc, they may not be entitled to know everything, or indeed anything at all.
It all depends on their position and yours, and also on any duties that may, or may not be, owed by you to them as a result. Imagine that a friend of yours has confided in you, but then another friend of both of you asks what you have been discussing. You have no duty to answer that question. It would be legitimate to fob them off by saying “Oh we were just chatting about this and that”. Failing to give an answer would be no lie, because there was no duty to answer them at all.