Final answer:
Crusoe's mastery over the English captain is derived from Crusoe's offer of protection against the captain's mutinous crew.
Step-by-step explanation:
The source of Crusoe's mastery over the English captain in Daniel Defoe's novel 'Robinson Crusoe' is best understood within the context of English and colonial attitudes during the period. Crusoe offers protection to the captain, who is at risk from a mutinous crew, in return for his submission. This aligns with Defoe's themes of mastery and servitude, highlighting the dynamics of power during the era of imperialism.