Some individual’s handwriting will display little difference in individual characteristics from the time that their handwriting had matured (usually in the late teens or early 20’s), until the time that they go to the grave. However, many individual’s handwriting will undergo at least moderate changes throughout a lifetime.
These changes whether seemingly slight or pictorially extreme, are brought about by any number of factors. Age and infirmity, medication, changing eyesight, or perhaps even a change in occupation can be the catalyst. Understanding what is written on a prescription may be a sophisticated game between the doctor and the pharmacist, but it is generally agreed that at one time most doctors were capable of writing in a manner that would allow the rest of the literate world to read what they had written. Accountants and police officers may change their handwriting in order to rapidly fit concisely printed lettering and numerals into small spaces on reports or ledger pages.
An individual who has had a normally fluid handwriting style may suddenly be overtaken with arthritis resulting in handwriting that may abruptly change and be unrecognizable as the same product of that individual. A stroke may change someone’s handwriting so severely, or even their ability to hold a pen, that the resulting product may be illegible and totally incomparable to the pre-stroke handwriting. Recovery from the stroke often returns the handwriting to near the original form.
Of course, there are a myriad of things that can cause external variation, from slamming your hand in a car door to ingesting drugs or alcohol. The list goes on indefinitely.