First, class. As Crusoe's father tells us at the opening of the novel, Robinson Crusoe's family is of the middle class. This class, according to old man Crusoe, is the best since it neither experiences the extremes of luxury nor poverty. Young Crusoe, though, strains against his father's class preference and decides to set off on his own.
Second, society. This is a novel very concerned with what makes a society. We begin with Crusoe alone on an island and gradually we begin to see the social order come together. First, there are his animal friends (Poll and company), followed by Friday, the Spaniard, Friday's father, and then the mutineering Englishmen. Pretty soon the island is its own little society with Crusoe at the head of it.
Humans are inherently social creatures.
Man is a self-sufficient individual.