What matters the most in ethics
There are many schools of thought which offer a response to this question. Consequentialist ethics emphasize, not surprisingly, the consequences of our actions. Deontological theories focus on the actions we perform, and whether they are consistent with a moral law or laws. Virtue theories of ethics focus on the character of the person performing the action.
When considering whether or not to perform some action, such as telling a lie, each school of thought would approach the decision from a different perspective:
1. Consequentialist: "What would the positive and negative consequences be if I told this lie?"
2. Deontologist: "Which moral rule or rules are relevant, and what do they prescribe?"
3. Virtue: "What would a person of good character do in this situation?"
I tend to favor virtue-based approaches to ethics, because I think that character is the most fundamentally important thing. However, I think that one should also consider the insights that can be gained by approaching a moral dilemma from all of these perspectives. Even if character is the most important thing in ethics, moral rules and the consequences of our actions are also relevant. While considering all of this is merely a starting point for finding our way through a moral dilemma, it's a good starting point.
In the modern world, we tend to emphasize emotions over rationality when considering what the ethical thing to do is. I believe that this is a mistake. Emotions are relevant, but approaching moral questions and dilemmas in a reasoned manner gives us the best chance to improve the world--and ourselves.
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