Certain serif fonts have distinctly different stroke widths for parts of certain letters (see WMVAU below) and there is a "correct" and an "incorrect" orientation. An example with Google Fonts Prata:

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What is this called and why does the top one look "correct" and the bottom one "incorrect"?

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    The short answer: stress.
    – Jongware
    Feb 19, 2016 at 20:57
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    I would love to see a font with all the stresses flipped, like your second image. It's so creepy! Feb 19, 2016 at 22:35
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    I'm one of those people. You know what I mean: innocently driving down a street and then AIGGHHH! Street sign in all caps Helvetica Narrow instead of one of the FHWA Series. Or going to the men's room in a restaurant and noticing the "W" on the women's door is backwards.
    – Jason S
    Feb 19, 2016 at 22:45
  • Wikipedia has a page on reverse contrast typefaces., with examples Also a great read: David Jonathan Ross' Backasswards (if only for its title).
    – Jongware
    Feb 19, 2016 at 23:50
  • Hmm. But reverse contrast typefaces represent horizontal instead of vertical stress. I'm talking about left-side vs. right-side.
    – Jason S
    Feb 22, 2016 at 18:14

3 Answers 3


It's called "Stress" and it's a remnant from when letters where hand-written by calligraphers and not yet printed by press.

A Brief Anatomy of Type I: Stress

The answer is really rather simple, and hails from the pre-printing days when books where still written by hand. During these times a tool called a calligraphy pen was used to produce hand-written volumes. These pens had a flat tip that resulted in a trademark thick-thin transition when the pen was angled a certain way.

After the printing press was invented by Gutenberg, letters were no longer written by hand with calligraphy pens. Instead, they were cast into metal representations of the letters that with ink could be used to ‘press’ the letters onto paper in an instant.

To give the ‘printed’ books the same authentic look as the hand-written volumes, the metal cast ‘letters’ used by the printing press were styled after the hand-written letters seen in volumes written with calligraphy pens. Thus, the thick-thin transition of stress is really just a throw-back to the days when books were written by hand.


History of Serif Typefaces

Serif typefaces originated from carvings in stone in Roman antiquity. The variation in thickness of the lines (or line contrast) and the angle that the thickness changes (the stress) comes from how the letters were carved in to the stone with a chisel.

From: A Typographic Workbook: A Primer to History, Techniques, and Artistry
By Kate Clair, Cynthia Busic-Snyder:

Angled or oblique stress in the letterform developed when a flat-tipped pen or chisel was held at an angle as the letter was drawn or carved. The thickest area of the stroke is the area of maximum stress[...]

Type Classifications

Serif typefaces can be grouped in to a number of classifications that, amongst other things, have different stresses and line contrasts.

Old Style

These typefaces date back to the beginning of the printing press and movable type. The contrast in thick and thin strokes is typically less than in later designed typefaces. Old style serif fonts have remained popular for setting body text because of their excellent readability on book paper.

Transitional Serifs

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The contrast of strokes in transitional serif typefaces was greater mainly due to the improvement of printing techniques developed in the 18th century

English printer and typographer John Baskerville established this style in the mid 18th century. [...] improved printing methods allowed much finer character strokes to be reproduced and subtler character shapes to be maintained. While the axis of curve strokes can be inclined in transitional designs, the strokes normally have a vertical stress. Weight contrast is more pronounced than in old style designs.

Modern (or Neoclassical & Didone) Serifs

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The contrast in thin and thick strokes in Modern serifs is much more extreme and with a vertical stress. This typically makes Modern serifs less suited (although not unseen) for body text and were therefore some of the earliest 'Display' typefaces.

When first released, these typefaces were called “classical” designs. Early on, however, it became apparent to printers that these were not updated versions of classic type styles, but altogether new designs. As a result their classification name was changed to “modern.”

All Images and (unattributed) quotes from: fonts.com - Type Classifications

  • 1
    so why is one side of the U or the M thicker than the other, if both are vertical strokes? (and it always seems to be the same even among different typefaces)
    – Jason S
    Feb 19, 2016 at 22:29
  • It has a lot more to do with a pen than a chisel. Reed and quill pens didn't ordinarily come to a point, which would wear out way too quickly and need to be recut every few strokes, they came to a "chisel point". Using such a pen with the right hand naturally makes upper-left-to-lower-right strokes heavy and upper-right-to-lower-left strokes lighter. Incised letters emulated written forms, not the other way around. Feb 20, 2016 at 16:48

Stroke modulation

Stroke modulation is how much the thickness of the stroke changes in different parts of the letter.

In traditional calligraphy, the brush pen is held at a constant angle as the letters are drawn, creating a stroke with a lot of modulation.

In more mechanical typefaces, modulation is often really low but our eyes are so accustomed to it, that even typefaces with little perceptible modulation are actually subtly modulated.

Source: calarts intro to typography

Or simply


Modulation means the usually cyclical and predictable variation in width of the stroke. In unmodulated letterforms, such as Helvetica, the stroke is always fundamentally the same width. In a Renaissance face such as Bembo or Garamond, the stroke is based on the trace of a broad nib pen, which makes thin cross strokes and thicker pull strokes. When letters are written with such an instrument, modulation automatically occurs.

Source: foamtrain.com/glossary


Also check this answer.

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