Maybe your handwriting is loopy and fat, or clipped and precise. Or maybe it’s tilted, scattered, curvy, or balanced. In any case, we tend to think these tiny but perceptible differences, resulting from little more than variance in nerve impulses through our fingers and hands, say a great deal about how we may have felt at the time of writing.

By many accounts, the study of handwriting — known as graphology — fits in somewhere between astrology and palm reading in terms of scientific rigor. Interpretations of an arbitrary trait, be it a birth month or an undotted j, produce wild guesses that turn out to be mostly true because we would prefer to believe over doubt. But not all of graphology is seen as pseudoscience. Handwriting is, after all, a motor skill. And motor skills tend to be the first to go when it comes to neurological disorders.

If eyes are the window to the soul, handwriting may be the window to the brain — at least in certain cases. Parkinson’s disease is a good example. A study conducted in 2013 found that, while clinical assessment remains the gold standard for diagnosis, the simple measurement of writing pressure and velocity could reveal with startling accuracy whether someone was healthy or showed early signs of Parkinson’s. Researchers made a correct prediction 97.5 percent of the time.

Or take depression. A study conducted in 2004 found that erratic velocity during writing often reflected dysfunction in the brain’s basal ganglia — an area that regulates, among other things, feelings of motivation and certain supplies of neurotransmitters. The majority of depression cases involve the same neural pathways, in particular a deficiency in the dopamine reward system. People suffering from depression tend not to see the value in rewarding activities, even those that used to give them great joy.

These two examples highlight the limits of graphology. Typical handwriting analyses look at the letters themselves, such as how far apart they are and other less obvious details, like whether a person loops the tail end of a lowercase d. Some analyses go even deeper. Kathi McKnight, a self-proclaimed expert in handwriting analysis, has found certain illnesses do crop up in the letters. Schizophrenia, for instance, features some letters that stand tall and others that like to wobble. McKnight also speculates so-called “downhill writing” could be evidence of depressive symptoms.

The trouble is that, from a research point of view, that’s all most graphology is: speculation. Asking someone to look at a piece of text and posing, “Do you think this person is optimistic or depressed?” may yield an intended answer, but not for any reason inherent in the handwriting. It’s arbitrary — in the same way you’d expect someone to assume a person wearing a blue shirt is more depressed than someone in a yellow shirt. As party tricks, graphology succeeds. But the second things get serious, it fails.

This isn’t to say science wouldn’t reverse its stance in the presence of new information. But no hard data has taken aesthetics into account. Clinical analyses look at the way people write. The aesthetics of the letters matter little, insofar as whether varied pressure causes some letters to look darker. Peering into the author’s head to know why he or she placed certain letters farther apart is impossible. All science can do is observe behavior; clinical study isn’t in the business of trying to interpret highly subjective forms of expression. A loopy letter here and there may be nothing more than a loopy letter. So let it loop. And leave diagnosis to the professionals.