There are many kinds of falsity—as many as there are kinds of evil—and there are many sources of things that are evil and of the falsities that they engender. Falsity that comes from evil, or evil-based falsity, is one thing; evil that comes from falsity, or falsity-based evil, which leads in turn to further or secondary falsity, is another. From just one false idea, especially if it is taken as a first principle, further false ideas flow in an unbroken series. There are falsities that are the result of cravings arising from our love for ourselves and for the world, and there are falsities that are the result of misleading sensory impressions. There are falsities that arise from what our religion has taught us and there are falsities that arise from our ignorance. There is falsity that contains some good and there is falsity that contains no good. There are also things that have been falsified. Everything evil has something false accompanying it. The falsity accompanying the cravings that arise from love for ourselves is truly evil; it is the worst kind of falsity.
Evil is heavy and falls into hell of its own accord, but this is not true of falsity unless it comes from evil. Good turns into evil and truth into falsity as they fall from heaven into hell because this is like coming into a dense and polluted atmosphere. The hells are surrounded by evil-based falsities, which look like storm clouds and unclean waters. The things that are said by the people who are in the hells are falsities that come from evil. Left to their own devices, people intent on evil cannot think anything but falsity. More on evil that comes from falsity and falsity that comes from evil.
Every falsity is something we can convince ourselves of, and when we have done so it seems to us to be the truth. We should therefore make sure something is true before convincing ourselves of it. We should be particularly careful not to convince ourselves of falsity in matters of religion because this leads to false convictions that remain with us after death. How damaging false convictions are.
What is good cannot flow into truth as long as we are intent on evil. To the extent that we devote our lives to what is evil and the falsity that goes with it, to that extent what is good and what is true are moved away from us. The Lord takes the greatest care to prevent truth from being joined to what is evil and prevent the falsity that comes from evil from being joined to what is good. If these pairs are mixed, the result is profanation. Truths put an end to falsities and falsities put an end to truths. Truths cannot be accepted on any deep level as long as skepticism reigns.
from New Jerusalem, Section 21