The human mind, which includes all meaning and truth we can make of things, is dominated by opposites. We think and experience ourselves and our world in terms of being and nonbeing, true and false, good and bad, self and other, hot and cold, and many other pairs of opposites.
As babies, we soon begin to see people and things as stable beings. This is called object permanence by psychologists, in spite of the fact that no people or things are permanent. We chew and shake things to test their being, permanence and solidity. As we begin to crawl and explore, we find that we can move through spaces, but not through things.
For the rest of our lives, as we move about in our world, we automatically judge things as present and spaces as absent. We polarize and separate being and nonbeing from each other exclusively and uncritically so that we can move quickly and efficiently in our environment. In the same way, we separate the true from the false and the good from the bad, automatically and uncritically.
However, when we do Philosophy, question our minds, and critically think about our thinking, we find that things are more complex than simple, exclusive opposites. Just as when we do Physics and Chemistry, we see that no things are absolutely hot or cold and there are many degrees on a continuous spectrum, in Philosophy, we see that things are more complex than simply being or not being, more complicated than categorically true or false. There are countless shades of grey between black and white, and we can always reinterpret things to gain a greater perspective.
It is useful to judge a table as solid and the space around it as empty if we simply want to walk across a room and avoid bumping into a table, even though no table is simply solid, nor is the space around it simply empty. If we jump on the table, we can show that it is not absolutely solid, and if we examine the space around the table, we find it is full of air, dust and light.
We do not encounter things that absolutely are or things that absolutely are not. An absolutely solid substance could never be made into a table, nor could we live in an absolutely empty vacuum, but it is useful to make snap judgements that are absolute and exclusive if we are uncritical and do not wish to change things. However, if we want to design a stronger table, or reduce the amount of dust in the air, it is useful to make complex judgements that are relative and inclusive, including opposites together as poles of a spectrum, not as separate categories.
In ancient India, Greece and China, philosophers argued that seeing being and nonbeing as opposite ends of one and the same thing is wise and useful. In ancient India, Buddha argued that all things are temporary, both being and not-being together as becoming, constantly changing while enduring. In ancient Greece, Heraclitus argued the same, saying that we can never step in the same river twice, and that we both are and are not. In ancient China, Laozi, the founder of Daoism, argued that just like a pot, or a wheel, or a room, all things are composed of being and nonbeing, and they would be useless if they were not both.
Our world is both closed and fixed, but also open and changing. Sometimes our judgements are right, and sometimes our judgements are wrong. Sometimes we judge that things are how they appear, and sometimes we judge that things are not how they appear. We judge that our judgements are right and wrong, continuously thinking and rethinking. We experience all of this before we learn to speak and use language.
We learn about what is and is not before we can say what is true and what is false. Across human cultures, we understand true and false in terms of being and nonbeing. Thinking deeply and critically about being and nonbeing, as well as the true and the false, exercises the mind and strengthens our thinking, which we use in every situation we question and change.