Apologies if this a bit too law specific for this subreddit.
To what extent is the US Constitution merely codification of what was English common law back when it was written? If it is to a significant extent, are there many cases where English common law has evolved but the US Constitution has not?
One example my friend had when posed this question was the right to a jury trial, which he said was common in England when the Constitution was written, but nowadays the US practices it as England did back in the 1770s while England has restricted the right to a much smaller set of cases. Based on my own research, this seems to be true, although it's completely out of my expertise. Are there other such examples?
The US constitution is partly a codification of the Rights of Englishmen, and partly a rejection of the English common law as it existed in 1789.
Much of the US constitution, such as the separation of powers first theorized by Baron Montesquieu, is a total rejection of the British theory of parliamentary supremacy. In the US, Congress, the judiciary and the President have defined powers, and the other two branches can't alter those powers except as permitted by the law.
This is totally different from the British system, which gives Parliament the power to make and unmake any laws as it sees fit. So, in theory (and sometimes in practice) Parliament explicitly retained the power to abolish traditional English liberties like the right to a jury trial.
The Americans, fresh off of the abuses of George III and his ministers, sought to place explicit limits on governmental power while ensuring that the national government could actually govern, unlike the Articles of Confederation. This is why, for example, Article 1, section 9 of the US Constitution bans ex post facto laws and bills of attainder, both of which were mechanisms used to retroactively punish conduct that wasn't criminal at the time of the act.