Complete the account of the design features.

The property that lets meaningless units combine into meaningful ones is duality of patterning. The property that lets a speaker refer to what is remote in time or space is displacement. The property that lets speakers produce sentences never heard before is productivity. And the fact that a child learns whichever language surrounds them is cultural transmission.

Learning the four in this order is useful because they answer four different questions: how the system scales, what it can be about, what it can produce, and how it is acquired.