Human nature is distinctive because of man's ability to communicate, to speak. It appears as though Isocrates may see this as a quantitative, rather than qualitative difference. Education should teach people to speak. Speech distinguishes us from animals. Speech was the key to political power.
Speech integrates many aspects of human ability.
Isocrates believed that education should not just teach us to think or just teach us to fight. It should make us well-rounded citizens. Education should help us survive and succeed in society. Education should prepare the elite to lead society. Isocrates' school tended to be aristocratic.