That said, most employers will not actually bother to negotiate with you. Many people just strike a bunch of crap out, sign, turn that in and hear nothing then think that they have negotiated. Unfortunately nothing makes the employer sign to that revision. So now you don't actually have an employment contract. Guess what? That means you fall under the default rules, which means in New York that a professional employee who is a programmer who writes programs in personal time on a personal machine is creating works for hire that belong to the employer. Congratulations on your great negotiating strategy. It earned you..nothing.

While negotiating can work, it is a lot more risky and a lot more work than having the good luck to live somewhere with saner rules.

At least in the UK (and yes, I have checked this with a lawyer) when I altered the contract before accepting a job, their paying me is deemed to be acceptance of my changes. I am surprised that the same doesn't apply in other common-law jurisdictions.

I admittedly haven't specifically checked this with a lawyer. My comment was based on a discussion with a former boss, but I cannot verify that it is correct.

However when I think through the principles of what makes a contract under common-law, it does make sense that payment would constitute agreement to the contract.