Reader question:

In this sentence – Researchers believe that the knock-on effect of people giving up smoking has been a major factor in the smoking decline over recent decades – what does “the knock-on effect” mean?

My comments:

We can perhaps best understand the knock-on effect by playing a game of domino bones.

First we stand pieces of dominos known as bones up on end and side by side. Then we knock the first piece down toward the second one. If we space the bones correctly, the first bone will fall onto the second bone knocking the second one down. The second then, as it falls, knocks on the third, and knocks it down as well. The third, of course takes down the fourth in the same manner and the same thing happens over and over again ad infinitum.

From this comes the term “domino effect”.

Or, in other words, chain effect.

Similarly, the knock-on effect refers to situations where one event leads to another. In the example from the top, when researchers attribute the decline in smoking to the knock-on effect of people quitting the fog, they mean to say that these quitters might have led to more people quitting the habit as friends and companions tend to influence one another.

However, I must point out that the domino bones might not be a perfect analogy because the knock-on effect often refers to indirect influences one event has on another. Unlike the domino effect, which is direct or chain effect – events linking to others like a chain – the knock-on effect is not always readily predictable, as demonstrated by media examples below:

1. Hundreds of air passengers faced further misery yesterday as the fall-out from the bad weather continued.

Seven flights into Liverpool were diverted to other airports and 10 were cancelled on Monday, leaving travellers stranded as they tried to make the bank holiday journey home after the Christmas break.

They were finally flown home yesterday.

But the disruption continued for easyJet passengers flying between Liverpool’s John Lennon Airport and Belfast when their flight was cancelled.

The knock-on effect of Monday’s problems was blamed.

- Travellers at Liverpool’s John Lennon airport hit by knock-on effect of heavy fog, LiverpoolEcho.co.uk, December 30, 2009.

2. Silver pieces of eight were another passport to trade, and, as the first object of a global economy, a key step in the history of money. Minted in South America from the end of the 15th century, they crossed both the Pacific and Atlantic oceans. So widely were these silver coins used that interruptions in the production of silver in Mexico and Peru had a severe knock-on effect. In Europe silver shortages led to a sudden massive expansion of the money supply and the hyperinflation of the mid-17th century. In China they helped cause the collapse of the Ming dynasty.

- A history of the world in 100 objects: Creative impulses, Economist.com, December 30, 2009.

3. Greece is set to unveil plans to control its public finances and struggling economy in 2010.

The spiraling debt problem in Greece is a major test of the common European currency, the euro, now in its twelfth year of circulation.

The markets wait to see how the Eurozone of 16-nations will respond to Greece's problems.

There are fears that prolonged problems in Greece could have a knock-on effect on other ailing European economies, such as Portugal, Ireland, Italy and Spain.

- Greece to unveil economy plan, NewStatesman.com, January 5, 2010.

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About the author:

Zhang Xin is Trainer at chinadaily.com.cn. He has been with China Daily since 1988, when he graduated from Beijing Foreign Studies University. Write him at: zhangxin@chinadaily.com.cn, or raise a question for potential use in a future column.

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（作者张欣 中国日报网英语点津 编辑陈丹妮）