Bolingbroke also plays the kinship card, telling York that he sees the image of his own father in him--"I see old Gaunt alive" (117)--and pointing out that if York had died instead of Gaunt, and York's son Aumerle had been similarly wronged, Gaunt would have acted as a father to him and helped him defend his rights.
York still cannot fully approve of an insurrection that chafes against his sense of values and order: "To find out right with wrong, it may not be" (144). Still, he is clearly swayed by Bolingbroke's arguments; he also realizes that he simply does not have the strength to repel his invasion. His decision to remain "neuter," or neutral (158), is tantamount to defecting to Bolingbroke's side--as he well realizes, particularly when he invites them to sleep in the castle for the night. Bolingbroke's political adeptness has won him, and cost Richard, another ally.