How do left-handed people write? Here are some common methods, and some uncommon ones.
First, for comparison purposes, here's a schematic showing how a right-handed person writes:
When a left-handed person tries to write like a right handed person, it doesn't work, because the action of their wrist makes the writing slant the wrong way:
This form of left-handed handwriting is usually called backhand; it's main disadvantage is that it tends to be illegible (since it distorts the letter forms). It also identifies the writer as left-handed, which some people prefer to conceal.
To make their handwriting slant the right way, the majority of left-handed people twist their wrists clockwise, so they're writing from above:
This form of writing, known as crabclaw, leads to smeared ink (or smudged graphite), prevents the writer from seeing what's been written, and is uncomfortable.
In school, left-handed children are sometimes encouraged to turn the paper slightly counter-clockwise, so that they won't have to twist their wrists so far:
A full 90-degree counter-clockwise turn of the paper puts the wrist back in the position analogous to that used by a right-handed person:
(but that's a little too radical for most elementary school teachers).
In a seldom-seen variant, the paper is turned 90 degrees clockwise, like this:
What's remarkable about this form of writing is that it is upside-down from all the others: the stroke away from the body produces a downward stroke on the paper! Because of this inversion, it is the hardest left-handed handwriting to learn (at least, the hardest to learn of those that produce readable writing -- see below for the one which doesn't). In many other respects, however, it is superior to the previous methods.
Leonardo da Vinci was left-handed; he solved the left handed writing problem by simply mirroring what a right-handed person does:
Of course, this produces mirror handwriting, but if you're mainly writing notes (or notebooks) for yourself, that is not such a disadvantage!