An excerpt from Universal Courtier’s Grammar by Denis Fonvizin, published in 1783.
Question: What Verb is conjugated most frequently of all at Court, and in what Tense? Answer: Even as at Court, so in the Captial, no one lives out of debt; therefore, the Verb conjugated most frequently of all is: to be in debt. (The appended Exemplary Conjugation is in the Present, since that is the Tense most frequently used of all.)
I am in debt.
Thou art in debt.
He, She or It is in debt.
We are in debt.
You, Ye are in debt.
They are in debt.
Question: Is the Verb ever conjugated in the Past Tense? Answer: Ever so rarely — inasmuch as no he or she pays his or her debts. Q: And in the Future Tense? A: The conjugation of this Verb in the Future Tense is in good usage, for it goes without saying that if one be not in debt yet, he or she inevitably will be.