The first sentences are those of the infant that are typically directed at other infants. These are the first words spoken into the world. These are the first words that are understood.
The next sentences are those which are typically directed at adults. These are the first words used by adults to communicate with other adults. And these are the first words that are understood.
That’s the way language works when the baby is a very young infant. The first spoken word is the first word that is understood. If we repeat that process for a baby that has not yet mastered language, most of the sentences that come earlier will be nonsense. But as they get older and more fluent, the sentences that are used in their first utterances become progressively more meaningful and more complex.
In the same way that the first word spoken is the first word understood, the first word spoken in a baby’s first language can be the first word that is understood. So as with the first word spoken, the first word that is understood in an infant’s first language becomes the first word that is understood.
This is one of those things that will only seem obvious if you have been around your baby’s first language for a while. As they grow older, there will be a gradual shift in their speech patterns. The sentences that are used to communicate in their first utterances will become progressively more meaningful and more complex.
A very quick example of this would be to ask if a person is using the word “go” when they are talking about making a decision or asking for something. When talking about making decisions or asking for something, they may use the word “go” to describe their decision or asking for it. When talking to someone, they may use the word “go” to describe their intention to ask or ask for something.
This is one of the reasons I love the internet (and the concept of a blog). I can always find out how a language is used in a single utterance. For instance, if I have a conversation with someone, I can find out if they use the word go when they are talking about making a decision or asking for something. I can also find out if they use the word go to describe their intention to ask or ask for something.