Another is this: setting grounds for why you will or won't enter into marriage. For example, a marriage isn't considered "freely entered" when one or the other party imposes a "condition" on the other. There is an entire section in most annulment forms by the dioceses in the United States which asks, "Were there any conditions for the marriage?" I get concerned when I see people making various "conditional" comments because, to me, it's a "red flag" that they may not understand the self-gift aspect that is important to the core of the marital commitment.
Have I confused everyone?
What type of condition are you referring to: past, present, or future? Is is known whether the condition is fulfilled prior to entering into the marriage?
A marriage may not be entered into contingent upon a future condition (i.e., I will marry you if you convert to Catholicism within two years). (Can 1102 sec. 1)
The Eastern code does not permit marriage subject to conditions regarding the past or present (i.e., I will marry you if I am the father of your child). The Latin code does permit conditions regarding the past or present (can. 1102 sec. 2); however, they are illicit (N.B. not invalid) without written permission of the local ordinary (can. 1102 sec. 3).
What the above leaves open are conditions about which the fulfillment is known prior to the marriage (i.e., I will marry you only after you convert to Catholicism).
A marriage is not valid if it is entered into under coercion; however, the existence of a condition is not prima facie evidence of coercion. In general, the person upon whom the condition is being imposed has the ability to decline both the condition and marriage. There may well be specific cases where this is not true, but one would have to demonstrate the presence of coercion or other impediment; the mere existence of a condition does not suffice.