The morality of a decision depends on the consequences. If the consequence is good then the decision was right but if they are bad then the decision was wrong. Within this category is Utilitarianism, which says that the best consequence is that people are happy, and so the best decision is one in which the most people are happy.
Although this seems like a reasonable guide, the reality is more complex. How do we know what the consequences will be? It’s impossible to predict every eventuality. And what about when the best consequence which will benefit the most people, depends on you doing something immoral? If you killed a man and then used his organs to save the lives of several others, then consequentially you did the right thing.
Consequentialism serves the masses and not the individual and so leads to situations like the Postcode Lottery wherein decisions are made and the budget set so that the majority of people benefit, but in doing so individuals may slip through the cracks.
Argues that certain things are always right or wrong, regardless of the consequences.
Deontology in many ways counters the inhibitions we may have towards consequentialism. So it would never be acceptable to murder an innocent person, even if doing so would be to the benefit of many others, or you should always tell the truth because lying is wrong. However, there is no room for flexibility in deontological ethics and so to stick rigidly to its principles could cause more harm than good in certain situations.