Gradual emancipation: Some Northern states adopted gradual emancipation laws that provided for the gradual freeing of slaves. For example, the Pennsylvania Gradual Emancipation Act of 1780 provided that children born to enslaved mothers after a certain date would be born free, and that existing slaves would be freed upon reaching a specified age.
Indentured servitude: Some slaves in the North were able to gain their freedom by completing a period of indentured servitude, which typically lasted for a specified number of years. During this time, they worked for their masters in exchange for their eventual freedom.
Individual manumissions: Enslaved individuals could sometimes negotiate with their owners for their manumission, or legal emancipation. This could involve paying a sum of money, performing a specific task, or entering into a contract that outlined the conditions of their release.
Legal challenges: In some cases, slaves were able to gain their freedom through legal challenges to their enslavement. For example, in 1783, Massachusetts Supreme Judicial Court ruled in Quock Walker case that slavery was incompatible with the state's constitution, leading to the liberation of many enslaved individuals in the state.
Underground Railroad: Some enslaved individuals from both Northern and Southern states were able to escape to freedom via the Underground Railroad, a network of secret routes and safe houses established to help enslaved people flee to free states and Canada.
These are just a few of the ways in which slaves in the North were able to acquire their freedom. The process was gradual and varied depending on factors such as the state's laws, the individual's circumstances, and the support they received from abolitionists and other sympathetic individuals.