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.

Like hairshirt.

Or tightrope.

Or oxytocin.

Sometimes the sentence can also be a paragraph.

Which is also a system.

Even if it, too, only contains one word.

Like:

Pauciloquence.

Or.