As your baby grows and adds more words to his vocabulary, there will come a time when your baby will start combining signed words into “sentences.” For our purpose a signed sentence is a combination of two or more words that occur in sequence and are somewhat related. For example, a baby might sign MORE + BIRD, or MOM + PLEASE. While the first sentence might seem abstract to carry any meaning, to your baby it represents a huge milestone. While your baby doesn’t understand that you can’t provide MORE BIRD, they are expressing what they want more of. This is huge.
Other times your baby might talk in sentences. Just before writing this, my son and I had a discussion about the SNOW + “plow (s).” He said BIG (signed and said) + SNOW + “plow.” Then he said SMALL (signed and said) and “man.” He was recalling seeing the sidewalk snowplow and road snowplow that had gone by a few days ago. He was combining 4-5 words (is snow plow one or two?) into a conversation. At the time he was well over 180 signed words and lord only knows how many spoken words – we had lost track (although my wife records everything so if anyone is curious we could probably find out!).
This anecdote illustrates how a baby is able to use what they have available to them to discuss their world. In this case, my son combined the words he could sign with those he could say. He also signed and said some of the words. He does this mostly out of habit and eventually, like all babies, drops the use of signs.
Signs are replaced with words over time because it’s easier for a baby at a certain point to pick up a spoken word. They are all around him and when not give a signing alternative, he adapts to the situation. Signing babies pick up language much faster than non-signers because they are more accustomed to sentence structure coupled with an advanced vocabulary. As soon as their vocal muscles catch up, they’re off to the races!