If divorce is the end of a marriage, annulment treats it as though it never existed.
A marriage can be annulled only when the law considers your marriage either void or voidable. Examples of void marriages—unions that aren't legal to begin with—are where there's bigamy or incest. An example of a voidable marriage is one that took place when the spouses were highly intoxicated. A spouse has to request an annulment if a marriage is voidable.
Here are five more situations where a marriage can be annulled.
A marriage can be voided if a spouse wasn't at the legal age to marry (under state law). Note that this basis for annulling a marriage might not apply if, after reaching legal age, the spouse who was under age still agrees to the marriage.
Court records show that in 1994, disgraced singer R. Kelly, then 27, married Aliyah when she was only 15-years-old. The marriage was quickly annulled.
Another type of marriage that can be annulled is one where either spouse lacked the capacity to consent. Examples of lacking mental capacity to consent to marriage include serious mental illness and being highly intoxicated. Questions sometimes arise in estate planning scenarios, where someone who is ill is claimed to have married someone else before dying, and then apparently left money or property to that new spouse. If the heirs of the person who died can get the marriage annulled on the basis that their family member wasn't mentally fit to enter the marriage, they might be able to claw back the money and property.
Finding out a spouse is permanently impotent is actually a basis for an annulment. However, it generally won't apply if the other spouse knew of the condition at the time of the marriage.
If either spouse was under duress at the time of marrying, the marriage can be unwound. Note that the duress has to be considered significant, such as carrying the threat of violence.
If a marriage is based on fraud, then it can be annulled. Kris Humphries famously filed to annul his 72-day marriage to Kim Kardashian on these grounds. An example of fraud would be where a spouse was addicted to drugs but didn't tell the other prior to marriage. However, if it's proven that the other spouse would have been willing to go through with the marriage regardless of the condition, the fraud would likely no longer be a basis to cancel the marriage.
Overall, there are circumstances where your ratifying (approving) the marriage after discovering a potentially invalidating factor means you won't be able to get an annulment. For example, you might ratify your marriage by continuing to live together with your spouse after learning about something that could invalidate the marriage.
Once a marriage is annulled, it's legally null and void. But there are other potential consequences that can come into play. For one, annulment could impact the ability to get alimony from the other spouse or affect rights to property acquired during the marriage. So, it's always a good idea to ask a family law attorney before making any decisions on this front.
Most annulments come about relatively shortly after a marriage, although there can be exceptions. Importantly, though, some states won't allow an application for an annulment after a certain time period.