Nothing in this world exists in isolation.
It is all linked.
And thus, every judgement we make - whether through pure thought, or experience - is due to the fact that we have an opposite point of reference.
For example, how can we know that something is hot, unless we also know something else that is cold (or, at least, colder).?
Yes, we can experience it ; as something uncomfortable - or, at it's extreme ends, even painful.
Our senses allow us to feel things, and react to them, without any real in depth knowledge.
But, if we are to actually know something - i.e understand it in more than just the physical level - then we cannot know one side of the coin, without also knowing the other too.
So; as we have said;
To understand heat - we must also understand cold, in order to compare, and contrast the two.
Same with darkness and light
Happiness and unhappiness
Virtue and immorality
And so much else too.
In truth, no two opposites are ever separate, no matter how far away they seem to our own experience. They are always just two ends of the same spectrum. Or two sides to the same whole (As summed up beautifully by the yin yang symbol).
So, even life and death, in this sense, are not separate.
Without some sort of life first
How could anything be said to die?
Without the concept of death
Would we even know we were alive?