There are many ways of modelling the same thing. Imagine you have a limited amount of money to fence in your yard.

An economist would say “you have a budget”. A cyberneticist or a linear programmer would say “you have a potentially binding constraint on your objective function”. A marxist might say “there is a contradiction between the size of your enclosure and the amount of fence you can buy”. A normal person would say “well there’s a tradeoff. I can fence in my whole yard or I can spend my money to go drinking on the weekends.”

All of these basically say the same thing. Marxists like to use dialectics which is a philosophical idea originally from idealist philosophers. When brought into the realm of materialist philosophy it gets called dialectical materialism.

Materialist philosophy is the idea that ultimately everything is matter and energy. Nowadays this gets called Physicalism sometimes. Idealist philosophy says that there are things which do exist but which are not material or energy. Ideas, gods, angels, conciousness, etc. Most people have a combination of these two ideas and so would accurately be called “Dualist” but internet leftists tend to use the term “Idealist”.

The simplest way to understand a “dialectic” is, I think, the following: At the start of the industrial revolution in England there were the old lords and a new wealthy business class. There was a conflict between them over the limited resources. There are only so many people to control, luxury goods to purchase, government positions to hold, etc. And these people have different interests. So a Marxist would say, when speaking in terms of dialectics, that “there is a contradiction between the aristocracy (landowners) and the bourgeoisie (business owners, capitalists)”.

Now obviously the relative strength of either side in this conflict can change. Maybe the business class start organizing and take more seats in parliament, maybe the lords begin raising their own knights and armies again, etc. A marxist would say that this change is actually not unusual but a key part of the system. They say that modelling things using dialectics and materialist philosophy means we can understand how things change and not be so surprised when they do. And when something does change they might say “the dialectic is in motion” or “the contradictions are sharpening”.

Ultimately the entire thing is fancy language from the 1800s that should probably be replaced because it’s alienating and bad for propaganda. “Conflict”, “tradeoff”, and “change” are much more sensible in 21st century English than “contradiction”, “dialectic”, and “motion”.