Massachusetts never passed any legislation to abolish slavery. The colony was afraid the slaves would be a welfare burden on the towns. As a result they stopped calling them slaves in the census. I know this because my ancestors owned slaves there after 1875.
oops - after 1785
It was called their state constitution, ratified in 1780.
In 1783 the Massachusetts supreme court ruled the new constitution outlawed slavery.
ladyjane: "The colony was afraid the slaves would be a welfare burden on the towns.
As a result they stopped calling them slaves in the census."
Massachusetts was a state, not a colony, in 1783.
Their supreme court ruling required existing slaves to bring suits in court for their freedom.
Slaves who did not sue for freedom remained slaves.
By 1790 Massachusetts had about 5,000 freed non-whites (no slaves) out of its 380,000 total population.
How many of those blacks continued to serve their former masters, now employers, we don't know.
But in the 1830 census Massachusetts did report one slave, so clearly, Bay Staters still understood the difference between slave & free.
ladyjane: "I know this because my ancestors owned slaves there after 1875 1785."
Were they paid a wage?
Were they free to leave?
Were they protected as citizens by law?
Then they were no longer slaves, they were free.
The Massachusetts 1790 census reported zero slaves.