Articulating what he wants to communicate most of the time
Speaking very clearly - although some still persist using 'baby talk', and some children cannot yet manage the sounds s, r, z, th, v, f
Understanding prepositions such as - around, before, out, through.
Asking questions beginning with "What" "Who" "Where" and "Why"?
Understanding the movement of time - that yesterday, today and tomorrow are different time periods.
Talk in complex sentences that are in the main, grammatically correct
Enjoying jokes.