Selden persuaded him to continue with his studies outside the law, and much of Hale's written work is concerned with theology and science as well as legal theory. Hale gained a good legal practice, although he allowed his Christian faith to govern his work. He sought to help the court reach a just verdict, whatever his client's concerns, and normally returned half his fee or charged a standard fee of 10 shillings rather than allow costs to inflate. He refused to accept unjust cases, and always tried to be on the "right" side of any case; John Campbell wrote that "If he saw that a cause was unjust, he for a great while would not meddle further in it but to give his advice that it was so; if the parties after that would go on, they were to seek another counsellor, for he would assist none in acts of injustice". Despite this, he was wealthy enough to purchase land worth £4,200 in 1648. He was in great demand; law reporters began recording his cases and in 1641 he advised Thomas Wentworth, the first Earl of Strafford, over his attainder for high treason. Although unsuccessful, Hale was then called to represent William Laud, the Archbishop of Canterbury, during his impeachment by the House of Lords in October 1644. Hale, along with John Herne, argued that none of Laud's alleged offences constituted treason, and that the Treason Act 1351 had abolished all common law treasons. John Wilde, arguing for the prosecution, admitted that none of Laud's actions amounted to treason, but argued that all of them together did. Herne, in his arguments written by Hale, retorted that "I crave your mercy, [Wilde]. I never understood before this time that two hundred couple of black rabbits would make a black horse!" The case against Laud began to fail, but Parliament issued an Act of Attainder which declared him guilty, and sentenced him to death. After the capture of Charles I, Hale was expected to defend him, and indeed offered to do so; the King refused to submit to the court, claiming he did not recognise its jurisdiction. Edward Foss writes, based on the statement of Charles Runnington, that it was Hale who actually provided the King with this defence, and that it was only because the defence prevented any counsel being called for the King that Hale did not appear in court. When it became clear that the King was losing the Civil War, and only Oxford held out, Hale decided to act as a commissioner to negotiate its surrender, fearing that the city might otherwise be destroyed.