The main difference is the action and effort involved, but other differences are the possible intent involved, and consequences. Very few moral systems demand action, except perhaps in very limited circumstances, while every moral system I know forbids some actions. The difference is quite obvious: requiring positive action will consume your entire life, while forbidding negative action leaves people free to do as they like, for the most part, and is also far easier to enforce.
There are circumstances where keeping secrets is roughly equivalent to lying in people’s minds. For example, as a witness in court, when being advised by an expert to do something that might have negative consequences (even if they deem it the best course of action), if there’s something obviously wrong but easily correctable (eg about your appearance, or you forgot your purse) you’d expect your friends to correct you and would be angry if you thought they noticed and said nothing. These seem to have in common that 1) there is clear information asymmetry, and 2) someone has been singled out.
I would also like to point out that proper lying by omission usually involves more effort than plain lying (if your objective was to change someone’s beliefs), because it will require a whole lot of true statements and misinterpretable statements to have the same level of effect as a blatant lie. And it would take even more effort to do this in a way such that it wouldn’t be obvious what you did if your mark found out the truth.
The main difference is the action and effort involved, but other differences are the possible intent involved, and consequences. Very few moral systems demand action, except perhaps in very limited circumstances, while every moral system I know forbids some actions. The difference is quite obvious: requiring positive action will consume your entire life, while forbidding negative action leaves people free to do as they like, for the most part, and is also far easier to enforce.
There are circumstances where keeping secrets is roughly equivalent to lying in people’s minds. For example, as a witness in court, when being advised by an expert to do something that might have negative consequences (even if they deem it the best course of action), if there’s something obviously wrong but easily correctable (eg about your appearance, or you forgot your purse) you’d expect your friends to correct you and would be angry if you thought they noticed and said nothing. These seem to have in common that 1) there is clear information asymmetry, and 2) someone has been singled out.
I would also like to point out that proper lying by omission usually involves more effort than plain lying (if your objective was to change someone’s beliefs), because it will require a whole lot of true statements and misinterpretable statements to have the same level of effect as a blatant lie. And it would take even more effort to do this in a way such that it wouldn’t be obvious what you did if your mark found out the truth.