The concept of dialectical contradiction can be rather simply understood.
The animal, including human, mind deals with physical reality in terms of fixed categories. An edible plant is an edible plant, fire is fire, etc. The human mind systematizes this characteristic in terms of logical systems that are based on expectations of consistency: A is A, the future is essentially like the past, elsewhere is essentially like here. That, in practice, allows humans to succeed in designing buildings that don't immediately fall down or spacecraft that go into orbit around distant planets. But objective reality is not a system of timeless, spaceless, abstract laws. It is also a perpetually ongoing physical process in which everything, insofar as it exhibits the concatenation of abstract qualities which allows it to be considered as *this* thing and not something else, has come into being from an *other* something and will in time be replaced by something yet other. But some other thing is precisely not *this* thing. So when the human mind seeks to comprehend anything at all with complete truthfulness (that is--complete correspondence between the abstract concepts defining that thing and the objective reality of which that thing is a concrete aspect) its full understanding must include not only the *this thing* but equally the *not this things* from which this thing emerges and into which it passes over. So if this thing is called A the not this things--whatever else they might be--must be called *not-A*.
So, to put it as simply as possible, contradiction is a necessary component not of physical reality (in which nothing is abstract or fixed) but of the human understanding *insofar as it fully and truthfully corresponds to objective reality.*
Shane Mage