Tracking that is too tight collides glyphs; too loose breaks the word

What it is

Tracking is a uniform add-or-subtract across a whole run of letters, not the pairwise tweak between two glyphs (that is kerning). Pull it too tight and adjacent counters kiss: r and n fuse into m. The word is still there; the letters are already the wrong letters. Push it too loose and intra-word gaps approach the word space, so a letter-run stops being one word and becomes a row of signs. Discriminability and word-hood sit on the same axis. They are not two unrelated knobs.

Why it happens

A Latin word is perceived through a gap ratio: small gaps inside the word, a larger gap between words. The visual system uses that ratio to carve a stroke stream into words. Tracking multiplies every inter-letter gap at once, so it moves the ratio. Negative tracking merges counters; confusable pairs (il, rn, cl) fail first. Large tracking lets inner gaps climb toward the word space, the segmentation cue fades, and reading turns into counting letters. Kerning only patches specific collision pairs (AV, To); it cannot rescue a run that has been uniformly squeezed or stretched. Monospaced type hides the problem: equal cell widths are not equal visual gaps, and a global track exaggerates the difference between W and i.

Where it stops holding

Display type that deliberately tracks until the word dissolves is graphic design, not paragraph reading; using that as a body strategy fails. Connected Arabic and Thai with combining marks do not share Latin’s gap structure, so tightness thresholds do not travel. Pixel grids swallow tracking changes smaller than a pixel: the same value visible in print is a no-op on a low-density screen. After user zoom, a tracking that was “just so” scales with type, and a setting that was slightly open at small size can split words once enlarged.

Applying it

• Let body tracking follow the face. Do not stack a global tighten or loosen on the paragraph style.
• Drop collision-prone words (million, clarity, rn pairs) at the target size and look: did counters become another letter, is the word still one lump.
• Track by role: display may tighten a little, small type may open a little. One value must not be shared by display and body.

Related

• Same group: F4.12.2 CJK usually needs no extra tracking; the em box already holds the gap · F4.12.3 All-caps and small type need extra tracking to stay distinguishable · F4.12.4 Uneven word spacing in justified Latin runs creates rivers
• Nearby: F4.08 Legibility and readability · F4.05 Alignment
• Search terms: tracking · kerning · letter-spacing