A good thing is a thing that has a positive effect on something else. It could be something that helps survival or reproduction, like food and water, or it might be something that gives pleasure, like a movie, or makes one feel better.
The idea of what is a good thing has implications for morality because it suggests what sort of things are worth doing, or at least worth trying. The question of what is a good thing is called the question of the good life and has occupied philosophers throughout history.
When used figuratively, the phrase good can mean that someone is being sincere, or honest, or is showing empathy or compassion. It also means that something is true, or that it is right. This use of the phrase has a long tradition in philosophy, but it is less common in modern language.
During antiquity, the concept of good was dominated by a desire for perfection. Some schools of thought leaned toward hedonism (the Epicureans, for example), but the more prominent school was perfectionism: a belief that human beings should seek to achieve excellence in all aspects of their lives.
For many people, the idea of a good person is based on certain traits: they are selfless, they don’t lie or steal, and they treat others well. The problem is, though, that even the most virtuous of us will sometimes do bad things. It might be a reaction to stress or trauma, or it might be a result of underlying problems like insecure attachment or unresolved feelings from the past. Regardless of the cause, these bad behaviors don’t make people bad; they just show that being good is hard.
The word good is also often used to describe things that are wholesome or pure. This usage is less a matter of ethics and more of aesthetics: it is generally considered to be pleasant or beautiful to look at, or it may have a beneficial effect on health, such as exercise or a diet of whole foods.
In addition to the attributive and predicative uses of good, there is a modal usage that has no relation to value. This usage is found in everyday speech and is sometimes considered a synonym for the adjective great, although it does not have the same meaning as the term wonderful.
A final point on the topic of good is that there are two main lines of inquiry in ethics involving this concept: the theory of the good and the question of what things are good. Philosophers have tended to take different positions on these questions depending on whether they are focused on the attributive or predicative uses of good. For instance, some philosophers have taken a naturalist approach to the good, while others, such as Franz Brentano, have developed theories that occupy a halfway point between Moore’s naturalism and the attributive theory of good.