Evil is a privation of good. No goodness without evil.
Im going to take the opportunity to address two arguments at once in a very compressed form, the simplified Yin-Yang concept of interdependent or complimentary opposites, loosely based on the Chinese philosophy by that name, and Leibniz and St Augustines arguments from the privation of good as applied to the Problem of Evil. I will argue that good isnt a necessary correlative of evil, and that evil and suffering are actions or events that can exist on their own account, unlike the concept of goodness which is logically dependent upon those negative actions or events in order for the concept to have any meaning at all. Before moving on we must be quite clear what we mean by evil. I think we can fairly sum up evil as any state of affairs actually or potentially harmful or destructive to sentient creatures causing them distress and suffering.
The tem goodness is dependent the term evil, and nothing is good unless it stands in relation to something that is not good, which is to say evil. Therefore evil isnt the absence of or a privation of goodness and to demonstrate that lets conceive of a world without evil, a conception that is logically possible. So now what do we have? We don't have evil, and nor do we have 'good', that is to say a state that exists in relation to evil, because evil doesn't happen toexist. But now can conceive of a possible world where there is only evil, in fact we will consider ourselves the creator of this possible world. We have created this evil world at the flick of switch, and note that as in the previous example the term itself would of course have no meaning to its inhabitants. But now, at the flick of a switch, we could put a stop to the evil. Those who did the killing would stop killing; those who did the robbing would stop robbing; and the volcanoes would stop pouring molten larva over the inhabitants. We've simply stopped the evil; we haven't introduced something called 'good'. The inhabitants didn't suddenly become 'good' to one another but simply ceased doing what they were doing previously. And the mountain wasnt evil and didn't become 'good' but simply stopped spewing forth the deadly larva. In the example I given above I've tried to show that 'good' doesn't exist in the way that evil exists. Now murderis evil, while not murder is simply the former not enacted. To say not murder is 'good' is simply to make a special plea for a state of 'goodness' when its very existence as not murder is conditional upon 'murder'. But lets try expressing that the other way round: for if we say if there was only good, all we are actually saying is that there wouldn't be any evil'. And a world without evil is just what it is, for without evil the term 'good' has no place. You can't be selfless where there is no selfishness, and you can't heal or console when there is nothing to be healed and no requirement for consolation.
We might ask what about love, isnt that the exception? Surely it is the ultimate goodness, an entirely positive state of affairs that can exist on its own account? Well, if we have a state of affairs where everybody loves and is loved, it isnt good unless it is better than some other state of affairs, where for example only some are loved or none are loved. This is really no different to a possible world where no person ever goes hungry; that doesnt make it a morally good world unless there are other worlds, such as this, where for some famine and want are a fact of life. What then if there is a state or condition in which everyone is to enjoy eternal pleasure and happiness, heaven for example, mustnt that be the epitome of good? In that case I would argue that the concept of good is being used in a different sense as pure pleasure and happiness, hedonistic and self-indulgent, but still stands in relation to the actual world of evil and suffering in which there isnt universal pleasure and happiness.
So when theists say there can be no goodness without suffering, as a means to justify the existence of evil in the world, they are correct but only to the extent that goodness requires evil to give it intelligibility and not because of it is a mutually necessary correlative. Evil and suffering are real states and conditions whereas good is just a positive term that identifies if/when those negative states or conditions are absent or overcome.