And it is an art because the graphologist has constantly to keep in mind the total context in which the writing is taking place: the ‘gestalt’ of the writing as a whole. Writing consists of three things – movement, spacing and form. A graphologist studies these variations as they occur in each of these aspects of writing, and attaches psychological interpretations to them. Expert graphologists can achieve a very high degree of accuracy.”
A bit of the history which explains that this is science.
“What is graphology? There was a first graphologist who came up with a work prior to Camilo Baldo’s, called Prosper Aldorisius, who invented IDEOGRAPHY. In his work “IDENGRAPHICUS NUNTIUS”, Aldorisius observed that people would write in different ways, concluding that it would suppose diversity in principles, qualities, depending on the writer’s nature. Camilo Baldo (1622), an Italian professor of philosophy of the University of Bologna, founded the School of Graphology of Paris and published: “Trattato come de una lettera misiva si cognoscano la natura e qualitá dello scrittore” “How to know, through a handwritten letter, the personality and nature of the author.” It is the first book that relates writing to personality. There were several scientific personalities of the era who tried to systematize Graphology, like Godofredo Guillermo Leibnitz (1646-1716), Johann Caspar Lavater (1741-1801), Johann Wolfgang von Goethe (1749-1832), Joan Louis Moreau de la Sarthe, (1771-1826), Edouard Hocquart (1787-1870).” You can read the full history here