body: While I am located in Europe, I am generally interested in how this is handled in different countries. This is not a current question, but more a theoretical question, about how the law "generally" works. I am aware, that different countries may have very different laws, but I would still like to read answers, regardless of the country.
  
  
  Let's imagine, that I get a contract, which claims something along the lines of "A admits, that all the code he has written for this company has always exclusively belonged to the company". 
  
  
  This is basically an admission to a fact.
  
  
  Let's imagine, that I have a condition for this admission and add: "This contract is void, unless payment of X happens before xx.xx.xx."
  
  
  Or let's even imagine, that I add "this contract is void, unless I get a bag of coke before xx.xx.xx.".
  
  
  1. Does me signing the contract count as an admission of the fact, even if my condition was not met?
  2. What if my condition was illegal or for some other reason invalid. Would this invalidate the whole contract or would it only invalidate the condition?
  3. If the counter party uses the contract in court as proof of my admission, would they need to sign the document as well in order to make the contract valid, thereby accepting the condition?
  4. Let's imagine an even more explicit situation: I am accused of murder. I make a deal, where I admit to the murder, but as compensation I demand a new car. The DA doesn't sign the deal or accept it, but later uses my contract signature as proof my guilt. After all it is a written admission.
  
  
  Please feel free to edit my question title, there is probably a better way to formulate this question.
  
  
  
title: Can an unacceptable / illegal condition in a contract be ignored without voiding the whole contract?