By listening to the context in which they are said. The Wikipedia quotes were simply to reaffirm the context in which both phrases are most likely to be used in

By listening to the context in which they are said. The Wikipedia quotes were simply to reaffirm the context in which both phrases are most likely to be used in. “All lives matter” is most likely to be used as a reaction to the Black Lives Matter movement. While “From the river to the sea” is most likely to be used in the context of Palestinian Liberation (sorry I’m repeating my self).