In Chapter 4, Jacobs uses ethos when discussing her family and Black Americans in general, characterizing them as hardworking and self-reliant people:
The brave old woman still toiled on […]. After a while she succeeded in buying Phillip. She paid eight hundred dollars, and came home with the precious document that secured his freedom. The happy mother and son sat together by the old hearthstone that night, telling how proud they were of each other, and how they would prove to the world that they could take care of themselves, as they had long taken care of others. We all concluded by saying, “He that is willing to be a slave, let him be a slave.”
The idea that anyone can will themself out of enslavement is troubling and simply untrue. Harriet Jacobs was not blind to this fact. To make sense of this moment in her memoir, it is helpful to recall that she was also writing a persuasive document designed to convince white readers to join the abolitionist movement. Many apologists for slavery argued that emancipation would lead to a major social and economic crisis. They claimed that formerly enslaved people would be at a loss for how to do business and support themselves without the so-called "protection" of their enslavers. Many of the white characters in Jacobs's memoir continue enslaving people under the guise of protecting them from worse fates, such as the loss of their homes. These enslavers, who think of themselves as kind and "benevolent," believe that manumission (freedom) will come at a price for the Black people they enslave: if a Black family has always lived on their enslavers' land and has never been able to amass their own wealth, it will be very difficult for them to make a comfortable life for themselves. This logic is not wrong, but it also does not account for the fact that these enslavers are perpetually stealing the wealth that these Black families could be amassing for their own benefit. "Protection" is far more harmful than helpful.
The passage above demonstrates that Black Americans are perfectly capable of making their own way, invalidating this argument in favor of "benevolent" enslavement. The emphasis on Grandmother's hard work to purchase her son's freedom demonstrates her fitness to make it in capitalist society. Self-reliance had always been part of the American ethos, so cultivating a self-reliant ethos for a Black family was a way of proclaiming that Black Americans were full Americans. This family pulls itself up by the bootstraps, just like the most iconic white American folk heroes and revolutionaries. Jacobs does not necessarily believe that it is possible to work one's way out of enslavement, but she nonetheless indulges the idea as a way of using ethos, knowing this rhetorical move will be convincing to white readers.