To cater for the possibility of two deaths occurring simultaneously or very close together, some people choose to insert a survivorship clause.
The period usually chosen is 28 days or a calendar month but can be up to six months.
Such a provision can prevent your money ending up where you did not intend it to go.
EXAMPLE
Jim makes a will leaving everything to his best friend Paul. They have known each other since school and have been firm friends for more years than either of them wishes to think about. Jim has never married and has no relatives to whom he feels any obligation.
Paul is married but his wife does not like Jim very much. Jim has always thought that Paul's wife is jealous of their friendship and he tends not to visit the house when she is there. One day Jim and Paul are driving to a race meeting together when an accident occurs.
Jim dies instantly but Paul makes it to hospital where he dies several hours later. Jim's will does not include a survivorship clause so his money and goods pass to Paul. Under the terms of Paul's will everything goes to his wife.
Paul's wife thus inherits everything Paul owned as well as everything Jim owned. If Jim had specified that Paul had to survive him by one month this result would have been avoided.
In this example Jim would, of course, have had to specify a recipient of his estate if Paul did not survive him by the specified period. He could, perhaps, have left his estate to a favourite charity or to another friend. See http://www.macmillan.org.uk/Donate/Legacies/Step-by-step.aspx
Perhaps you might consider taking legal advice from a solicitor about making a will if any of the following apply to your circumstances:
see: Making a will - The Law Society. Please note that will making differs in Scotland and this website currently deals with English law.