Account is still available, but actions in account are very rare these days, for in the evolutionary struggle for survival, indebitatus assumpsit, though formally an action based on tort, has evolved to fill the remedial niches formerly occupied by both account and the greater part of debt. But enough of these Just So Stories. So, after looking a little more closely at the evolution of the actions of debt and detinue, we shall turn our attention to three cases, one involving account, one involving conversion, and one involving the use of indebitatus assumpsit to avoid unjust enrichment. And since detinue has, in the United States, pretty well been replaced by statutory actions of replevin, it is also hard to find modern cases expressly sounding in detinue. It is, however, clear that the action is restitutionary in nature, since the action is in form one to recover goods that have been detained by the defendant, and since in practice the successful plaintiff does recover either the goods or their value.
Debt is also restitutionary and has always been recognized as being so.
This is somewhat obscured by the modern tendency to divide all civil actions into actions on tort and actions on contract. Since, however, an action of debt lies on an obligation to pay a fixed sum created by a judgment or a statute it is apparent that the action is not necessarily based on contract. The distinguishing feature of the action of debt that it can only be brought to recover a sum certain. Unliquidated sums could not traditionally be recovered in debt. Historically debt and detinue were the same action commenced by the same writ.