I know what you're thinking: "How in all the worlds do you pronounce 'physiognomy,' and why does this look like a regular post and not a word definition?" Or, if you're of a whimsical bent of mind, "Does 'physiognomy' have something to do with gnomes?" (Kind of.) I suppose I should start at the beginning:
Definition: facial expression, regarded as indicative of one's character; the art of judging character based on one's physical appearance; the general form or appearance of something.
Origins: Actually, yes, 'gnome' and 'physiognomy' are related by way of the Greek root gnomon, 'one who knows,' from another Greek word, gignoskein, 'to come to know.' (And "gnomon" is itself an English word, which refers to the part of the sundial that casts the shadow.) For more thoughts on the origins of "gnome" and "physiognomy," here's an interesting article.
Now onto the literary application: Physiognomy is, simply put, the act of a judging a book by its cover. It used to be regarded as a science in the eighteenth and nineteenth centuries, similar to phrenology, the "science" of feeling the bumps on one's skull to determine one's character. Nowadays both of these are regarded as pseudosciences, but even if physiognomy isn't a metric we should rely on in real life, we can use it to our advantage when we write stories.
When you see someone walking down the street, you notice certain attributes (clothing, gait, and such) and make certain judgments--no matter how open-minded you may be. This is necessary for human survival: We need to be able to identify quickly our friends and our potential foes. It is also useful to human society: Based on the slogan on one's t-shirt or how much makeup one wears, we can make an educated guess at whether we would get along with them or not. Whether or not these guesses are accurate, we make these small judgments of character every day without thinking about it. That's physiognomy.
The same process occurs, in a slightly different manner, when we watch TV. You can tell the tall, handsome, well-dressed man is the love interest before he says a word to the main character. There is a difference between the figure or a librarian and that of a yoga instructor which we notice immediately: Before we know the characters' careers, we form ideas of what they might do based on their perceived level of activity.
Readers do the same thing in stories, and that is why physiognomy (in a broad sense that also includes dress, neatness of appearance, and other physical considerations) is useful to writers in two ways:
1. Add concrete description. Say you want a character to appear confident without saying "She was confident." Show how she walks: erect, shoulders back, at a leisurely yet purposeful pace. In this way, physiognomy helps writers show instead of tell.
2. Take control of the reader's expectations. Say one of your characters is a secretly a villain, but you want him to seem good for the time being. Make him relatively attractive (but not too handsome--readers eye "perfect" characters with suspicion), put a genuine smile on his face, and give him open body language. It takes actions, of course, to make a complete character, but appearance does a lot to convey personality, for better or worse.
Take physiognomy into consideration the next time you develop a character. Everything from the shape of his nose to the color of her eyes says something to readers. Add well-placed physical description, and guide or subvert expectations as you please.
