Every sentence is a system.
It has to have something that delivers the desired outcome.
It needs something or someone to deliver the outcome to.
It needs a source of energy.
It has to have something connecting the source of energy to the something that delivers the desired outcome.
It needs a guiding purpose.
And it needs to gauge how well the purpose is being met.
Even if the sentence only has one word.
Sometimes the sentence can also be a paragraph.
Which is also a system.
Even if it, too, only contains one word.