R.,
Our daughter was the same and is now 4 and catching up great. I wouldn't worry to much yet.
Here is something I found in a reference book I have called the "Encyclopedia of Children's Health":
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Communication is the process by which information is exchanged between individuals. It requires a shared understanding of symbol systems, such as language and mathematics.
Description
Communication is much more than words going from one person's mouth to another's ear. In addition to the words, messages are transferred by the tone and quality of voice, eye contact, physical closeness, visual cues, and overall body language. Although the verbal milestones follow one another in roughly the same sequence for all children, there is significant variability from child to child on when the first word is spoken and the first sentence is composed.
Language employs symbols—words, gestures, or spoken sounds—to represent objects and ideas. Communication of language begins with spoken sounds combined with gestures, relying on two different types of skills. Children first learn to receive communications by listening to and understanding what they hear (supported by accompanying gestures); next, they experiment with expressing themselves through speaking and gesturing. Speech begins as repetitive syllables, followed by words, phrases, and sentences. Later, children learn to read and write. Many children begin speaking significantly earlier or later than the milestone dates.
Parents should avoid attaching too much significance to deviations from the average. When a child's deviation from the average milestones of development causes the parents concern, a pediatrician or other professional may be contacted for advice.
Toddlers one and two years of age experience the world through the physical senses. Language development for toddlers includes: using two-word combinations, taking turns speaking and listening, using the word no frequently, and using gestures to express needs and desires.
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It sounds like your son is very bright and maybe the two of you are so well connected that not a lot of words need to be spoken between you to get his needs met. Try introducing him to different and varied social situations that allow him to stretch his need to be more verbal. If your still having concerns in 6 or 8 months - have him checked out with a doctor.
Good luck, I hope this helped.
S.