Abstract knowledge

Chapter 5 endnote 36, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

As [children] learn a concept such as “Anger,” they can predict and give meaning to other people’s movements and vocalizations ​— ​smiles, shrugs, shouts, whispers, tightened jaws, widened eyes, even motionlessness ​— ​as well as their own bodily sensations, to construct perceptions of anger. [...] This may be when children begin to learn that emotions cause actions.

This may be when abstract knowledge begins to develop. In the past, scientists have assumed that when infants demonstrate abstract knowledge—what it means for one event to “cause” another (the purely mental concept of causality)—this knowledge must be innate; but abstract knowledge can be learned very quickly, particularly in the presence of language.