On this show , we explore the world of American English . We talk about common expressions , where they come from and , most importantly , how to use them . Today we talk about behavior and self-control . There are ways of behaving that almost everyone considers normal or comes to expect . Children learn very early that some behaviors are more accepted than others . They learn how to control themselves and how to behave in certain situations . This learning continues into adulthood . Well , for most people it does . Not everyone behaves how they are expected to . So today , we talk about loose cannons ! A good word to describe a loose cannon is unpredictable . You never know how an unpredictable person will act in any given situation . But not all unpredictable people are loose cannons . Some people often change their minds about things . Or they surprise you by doing something they do not usually do , or that is out of character . We could describe such people as changeable , uncertain or -- here's a good word -- fickle . But I would not describe a loose cannon as fickle . Fickle people can be annoying but they are not usually dangerous . Loose cannons , on the other hand , are often unpredictable in violent ways . So , they can be very dangerous ! A good word to describe a loose cannon is volatile , or likely to explode ! So where did the expression “loose cannon ” come from ? Because of their weight , cannons have to be firmly tied down . Hundreds of years ago , cannons were often found on battleships . Sometimes a battle at sea with another warship or a storm would free them from their mounting . As you can imagine , a loose cannon rolling around could do serious damage to a ship and her crew . We can say the same about a person who is a “loose cannon .” Loose cannons , both the guns and people , are difficult to control . Their unpredictable behavior can cause problems for them and others . Family , friends , coworkers or larger groups , such as a sports team or political party can all be affected by a loose cannon . You are not sure how loose cannons will react to something . They could get angry , losing their temper at the smallest thing . Now , let's hear how these words and expressions can be used . So , local officials are meeting tomorrow night to decide whether or not our neighborhood gets a new school . We need to bring some people who can speak about this issue . Let's ask D.J . from across the street . He works at a school . He's a loose cannon ! One minute he seems fine , but the next he is shouting and hitting the table . What about Helen ? She's more unpredictable and volatile than D.J . One wrong word and she could explode . They are both loose cannons . Well , can you think of any other people ? How about Matthew ? The city council banned him from attending any meetings for one year . Are you serious ? At the last meeting he completely lost his temper and actually hit someone ! I'm feeling our neighbors are a collection of loose cannons . Maybe … let's not tell them about the meeting . They will do more harm than good ! Is there someone in your life who is a volatile loose cannon ?