You probably have to read this more than once to actually understand it. We cannot appeal to this deux ex machine to explain the convergence of our ideas and the truth about the world. This refusal to admit a general intelligence is a fundamental error in Chomsky's thinking. The 'argument' is based on stating that supporters of general intelligence cannot say on what principle it is based. This is nonsense, because the existence of general intelligence is not dependent on whether we understand its underlying principles or not.
Children have the capacity to acquire the number system.
They can learn to count and somehow know that it is possible to continue to add one indefinitely. They can also readily acquire the technique of arithmetical calculation. If a child did not already know that it is possible to add one indefinitely, it could never learn this fact. Again, you probably need to read the last two sentences more than once to comprehend what they actually say. Chomsky does not bother to tell us why would the child assume it is the end of the story, and does not base this statement on supporting evidence.