The Ballad of Subsequent Impossibility:

For those who remember Paradine v. Jane (1648) from your contracts classes; if I'm not mistaken, it's still in some casebooks, or has been until recently:

1. What the parties said.

Jane refuses his rent to pay.
'I have no kine, nor corn, nor hay;
Rupert the alien came my way,
     Cared not a button
For rights of property. No, the thief
Carried my harvest every sheaf,
Turned my oxen into his beef,
     Sheep into muttion.

'Fields are ravaged and homestead burned,
Out of my lands by the alien turned,
Nought can I pay where nought is earned,
     So I go free.'
'No,' said Paradine, 'I'm afraid
I must ask you for rent unpaid:
No conditions in lease were made.
     Hear Court's decree.'

2. What the Court said.

'This is no duty by law created,
Else had vis major the charge abated.
This is a contract. The terms are stated.
     Nought do they say
Of risks excepted which loss prevent,
Nor yet of conditions subsequent.
Such should be mentioned if such were meant;
     So Jane must pay.'

3. The rule and its exceptions.

Thus and well do the Courts decide.
Make conditions lest ill betide,
Else by your promise you must abide.
     Yet I'll remind you,
Where the thing to be dealt with is destroyed,
Or Parliament makes your promise void,
Or illness shatters the skill employed,
     Contract don't bind you.

With these exceptions, you can't be heard
To say that, from things which have since occurred,
It isn't convenient to keep your word.
     Unto the letter.
And, with this knowledge, I may opine
That the case of Jane and of Paradine
Will never be either yours or mine;
     No! we know better.

From Sir William Reynell Alson, Ballads en Termes de la Ley (1914).