
posted 3rd May 2024

Ping! A message lands on your phone. Ayesha is inviting you to her party on Saturday night. Great! Ayesha's parties are always amazing. You're about to accept when ... Ping! Another message lands on your phone. Your best friend Ben has got tickets to see your favourite band on Saturday night.
Ayesha's party and Ben's gig are both happening at the same time. You can't go to both. You're going to have to choose. Choosing means giving up one of two things that you really want - Ayesha's party or Ben's gig - in order to have the other thing. Whichever decision you make, there will be a cost. Not a cost in money; a cost in the opportunity to attend Ayesha's party / Ben's gig.
This is an example of what economists call an opportunity cost. The opportunity cost is a calculation of the value of whatever you have to sacrifice when you are making a choice between two mutually exclusive alternatives. In the example above, you have to decide which has the more value for you: partying with Ayesha or gigging with Ben?
How can you use the idea of the opportunity cost in debating? Here are a couple of examples.
The motion is This house would abolish homework. You're the opposition. The proposition has been arguing for the academic benefits of homework. You agree that there may be academic benefits, but there is also an opportunity cost. All those hours schoolchildren spend doing homework are hours they could be spending seeing their friends; playing sport; doing hobbies; hanging out with their family. Homework reduces children's opportunities for all these enriching activities.
The motion is This house would introduce a year of military service for all 18 year olds. You're the opposition. The proposition has been arguing for all the benefits of military service for young people - how it teaches them self-reliance and a raft of valuable skills. Yes, you reply, but there is an opportunity cost. That year could be spent studying, or training for a job, or starting a job, or travelling the world. Military service means at best postponing, at worst losing, all kinds of opportunities at a time of life when a young person should be finding out about themselves and the world, not standing to attention while being shouted at by a sergeant-major.
Introducing financial cost as a reason for not following a course of action is not normally helpful in a debate. Almost every course of action has a financial cost; the question is not how much something costs, but whether it is the right thing to do or not. However, opportunity cost, in which following one course of action means not being able to follow another, can be a very helpful dividing line in a debate. Is the benefit of the action proposed greater than the opportunity cost entailed by the action? A great many debates turn on this question.