Final answer:
George Washington believed that the tendency to form political parties is a natural aspect of human behavior that cannot be eliminated but urged caution in managing their influence to preserve national unity.
Step-by-step explanation:
When George Washington remarked that the spirit of party is inseparable from human nature, he was expressing a belief that the tendency for people to form groups or political parties with common interests is a basic aspect of human behavior that cannot be completely eliminated. Washington conveyed a concern about the divisiveness and potential harm that could arise from political parties and factions, particularly regarding their negative impact on maintaining national unity. He warned that while the formation of parties is a natural outcome of human nature, it was the responsibility of the citizens and leaders of the nation to be vigilant and to manage their influence wisely to avoid the 'mischiefs' that such spirit of party could bring to the republic.