The ability to make a will is a right given by state statute. If you don't make a will, the state law of intestacy determines who gets your property. If you do make a will and things in your life change, sometimes state law causes a change in your will. This is called "modification by circumstances." In these cases, what your will states is overridden by the state law.
For example, if you make a will and then get divorced, Pennsylvania law provides that "[i]f the testator is divorced from the bonds of matrimony after making a will, any provision in the will in favor of or relating to his spouse so divorced shall thereby become ineffective for all purposes unless it appears from the will that the provision was intended to survive the divorce." In other words, unless the will states otherwise, a divorced spouse is not entitled to take under a will even if he or she is named as the primary beneficiary. This can be a trap because if death occurs after the divorce is filed, but before it becomes final, the parties are still married and the surviving not-quite-divorced spouse would take under the decedent's will unless adequate grounds have been established for the divorce.
The divorce, however, cannot be fraudulent. How can divorce be fraudulent? A recent New York case comes to mind. David and Vivian Dowers were married for 30 years before his death. David died at age 65. Vivian was still mourning his death when she discovered a divorce decree from 2002 stating that she had abandoned him and that they were legally divorced. They had always lived together and she had received absolutely no notice of the proceeding. She was stunned that he could obtain a divorce without her even knowing about it.
The court decreed that the divorce was a fraud and David and Vivian were not divorced. Apparently, David wanted to give his pension and life insurance to someone else, probably his children from a prior marriage, thus, the attempt at the stealth divorce. Had the court upheld the divorce, the state's statute would have given his estate to his children.
In another twist, while the divorced spouse doesn't take under a pre-divorce will, if children of the divorced spouse are beneficiaries, the law does not modify the will in that case and even though the parent is divorced, the children would still be beneficiaries under the former step-parent's will.
Here is another example: A person makes a will and then gets married. In Pennsylvania, marriage does not revoke the will. However, Pennsylvania law provides that unless the will is made "in contemplation of marriage," the surviving spouse, even if he or she is not mentioned in the will, gets what would be his or her intestate share of the deceased spouse's estate. The spouse has another right, that of electing against the will if he or she has been disinherited. One would need to figure out which is bigger, the intestate share or the elective share.
Making new wills either just before or just after marriage is always a good idea. If done just before the marriage, it is important to state in the will that it is being executed in contemplation of marriage and to name the intended spouse. That prevents the law from imposing its own "codicil".
If the marriage will be a second marriage and a pre-nuptial agreement which determines distribution upon divorce or death is executed, the minimum action needed to prevent the "Modification by Circumstances" law from negating the agreement is a no-change codicil that states that it is being executed in contemplation of marriage to the intended spouse and then reaffirms the last existing will.
If you kill your spouse, or any other person whose will gives you a benefit, you cannot inherit. This is called the "slayer statute" and prevents a murderer from benefitting from his or her crime.
In Pennsylvania, children have no right of inheritance. A parent is free to leave a will that disinherits a child. However, that is not the case for a child born or adopted after the execution of the will. Regarding birth or adoption, the law states that "[i]f the testator fails to provide in his will for his child born or adopted after making his will, unless it appears from the will that the failure was intentional, such child shall receive out of the testator's property not passing to a surviving spouse, such share as he would have received if the testator had died unmarried and intestate owning only that portion of his estate not passing to a surviving spouse."
If this is not what you have in mind for your estate plan, you need to either make a new will or make a codicil stating your intention to exclude any child born or adopted after the execution of your last will.
There used to be a prohibition in the law against any bequests made to charity within 30 days of death, the theory being that such gifts were easily coerced from someone on their death bed. That provision was repealed in 1976.
The bottom line is that when you experience a change in life, you should review your will and other estate planning documents to make sure your intentions are carried out.