I'm not sure! I'll try and find out for you.
A short plank of wood is less easy to bend or break compared to a long plank.
2 short planks placed on top of each other becomes denser or thicker.
Thick can be used as an expression to describe someone of a lower intelligence.
So, two short planks together = rather thick......
This is what I thought, but there is usually more to the sayings than that. The story about the planks in the mud also makes sense. I like that reason better!
Another reason could be from the 1st World War.
The British artillery guns had to be supported on two short planks of wood to stop sinking into the mud.
To this day the British Royal Artillery are call planks and within military circles it is taken for granted that their IQ or intelligence is not that high.
So one can say that the phrase thick as two short planks, has possibly come from the battle fields of France and over time has become a common use in everyday English. Especially after many of the British Royal Artillery went back to normal working life after the 1st World War, where the saying would have been spoken in wider circles (community).
Hope this is of use :)
The history of words and idioms is an interesting subject. Teacher Johnny is studying linguistics at university. He's written a couple of blogs about the history of the English language if you are interested! I don't think anyone is as thick as 2 short planks all the time. I think that many of us (myself included) have our moments when our brains are switched off!
Check out John's blogs here:
It is usually used to describe the personality of someone. Someone can be as thick as 2 short planks all the time or just for a moment! Teacher Johnnie Simpson will be happy to answer your questions. :)
Some of our greatest and richest superstars have been as thick as two planks
just put example,i don't mean to offend someone.O(∩_∩)O~
That's very true here as well Una!