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I am sorry to hear about this situation. On this website, I do not always get to give good news, and this is one of these times. I understand that hearing things less than optimal is not easy, and I empathize. Thanks in advance for not "shooting the messenger."
1) There is something called the parol evidence rule. What this means is that if there is a verbal agreement and a written agreement about the same thing, then the written agreement is presumed as valid and overrides the verbal agreement. It is possible to introduce verbal agreements in cases of fraud, etc, but it is very hard to do, and especially if the other party (James) flat out denies stating this, as he likely would.
2) Since there is no proof of James stating this, then the written agreement is taken as is, meaning it is enforceable.
3) Now, the breach of contract is by your son. And in breaching contract, he is liable for the remaining rent. However, while it is presumed that he is liable for all the remaining rent, he can claim an affirmative defense of mitigating damages. A Plaintiff has a duty to mitigate damages (see McCord v. Green, 362 A. 2d 720 - DC: Court of Appeals 1976 for general discussion). This means that the landlord has to then make reasonable attempts to re-rent the property, and if he does, then your son should only be liable for the time that the property stood empty during his broken lease period. If the landlord did not make reasonable attempts to re-rent, then the Court may at its discretion minimize the liability, although not all of eight months, but possibly 2-3, etc, depending on the Judge.
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