Mirror writing, writing from right to left with flipped letters, is harder than it looks. Try it and see how well you do.
By writing in the reverse direction it’s possible, but fiendishly difficult, to create a mirror image of the words we are producing. Some people believe that this style of writing may once have been a crude attempt to create a kind of code. It’s even been claimed that Leonardo, who made most of his notes using mirror writing, may have done so in an attempt to stop his rivals from stealing his ideas or to prevent some of his more controversial beliefs from reaching the attention of the Catholic Church, who could be entirely humourless in these matters.
A simpler explanation is that, as a left handed person, he wrote from right to left in order to avoid smudging the ink on the page. Some left-handers do this readily.
Brain scans have shown that there are some important differences between the brains of left and right handed people. While right handed people tend to develop specific parts of the brain which are devoted to particular tasks, left handers, such as Leonardo, demonstrate far greater flexibility and much less specialisation – they also tend to recover from strokes far more quickly.
Incidentally, the technical term for left-handedness is sinistrality, which derives from the Latin word sinister, meaning “left”. This would suggest that Leonardo was a truly sinister artist.