What term describes a party who is incapable of entering into a valid contract on his own part?

The term used to describe a party who is incapable of entering into a valid contract on their own is "incompetent." This refers to individuals who lack the legal capacity to consent to a contract due to reasons such as age, mental incapacity, or intoxication. For a contract to be enforceable, both parties must have the ability to understand its terms and consequences; otherwise, the agreement may be deemed void or voidable.

In contrast, the other terms presented do not apply in the same context. For instance, "increment" refers to an increase or addition, often in a quantitative sense, and is not related to contract validity. "Inchoate" typically means incomplete or not fully formed, which does not address the capacity to contract. Finally, "investor" describes a person who allocates resources, typically money, into various assets with the expectation of generating a profit, but this term does not pertain to one's ability to enter into contracts. Understanding these distinctions highlights why "incompetent" is the correct choice in the context of contract law.