The claim argues that enslaved people performed enormous quantities of labour for which they were never paid. That labour produced wealth. The wealth was captured by slaveholders and by the states that protected the institution of slavery. Because the labour was stolen, the proceeds of that labour are owed to the descendants of those who performed it.
The argument is presented as analogous to theft: if someone steals your property, you are owed its return or its value. The labour of enslaved people was taken without consent and without compensation. The value of that labour, compounded over generations, constitutes a debt that has never been acknowledged or paid. Reparations would be the acknowledgment and partial payment of that debt.
In economic terms, advocates calculate the total unpaid labour by estimating the number of enslaved people, their working hours, and what their labour would have cost at market rates, then applying compound interest from the date of the labour to the present. Different calculations produce figures ranging from hundreds of billions to trillions of pounds.
