Double arrows (⇐, ⇒, ⇔) in HTML
The double stroke arrows mean implication and equivalence in logic. Their named references are ⇐, ⇒ and ⇔, which differ from the single arrow names only by a capital letter.
At a glance
- Character
- ⇐ ⇒ ⇔ ↔
- Named entity
- ⇐ ⇒ ⇔ ↔
- Decimal reference
- ⇐ ⇒ ⇔ ↔
- Hex reference
- ⇐ ⇒ ⇔ ↔
- Unicode code point
- U+21D0, U+21D2, U+21D4, U+2194
- Unicode name
- LEFTWARDS, RIGHTWARDS and LEFT RIGHT DOUBLE ARROW, LEFT RIGHT ARROW
- In the entity reference
- Arrows
In detail
The entity names here are the sharpest edge in the whole arrow set. The single stroke arrows are ← and → in lower case; the double stroke ones are ⇐ and ⇒ with a capital A. Character references are case sensitive, so lowercasing your generated HTML converts every implication sign into a plain arrow, which changes a logical claim into a direction and does so silently.
The right pointing double arrow means implies. It asserts that if the statement on the left holds then the statement on the right holds, and nothing about the reverse. The bidirectional double arrow means if and only if, which asserts both directions at once and is a much stronger claim. Substituting one for the other in a specification is a real error, not a typographic one.
The single stroke bidirectional arrow at U+2194 is a different thing again. It has no logical meaning; it indicates a two way relationship, a resize handle or a horizontal span, and it is the one you want for a user interface rather than for a proof.
In technical writing outside formal logic, these arrows are often used loosely to mean leads to or corresponds to. That is fine in a diagram legend, less so in a requirements document, where a reader with a mathematical background will read the strict meaning and hold you to it.
Examples
<p>n > 4 ⇒ n > 2, but not the reverse.</p>
<p>A set is empty ⇔ it has no members.</p><p>← is U+2190 and ⇐ is U+21D0.</p>
<p>→ is U+2192 and ⇒ is U+21D2.</p>
<p>↔ is U+2194 and ⇔ is U+21D4.</p>A lowercasing step anywhere in your pipeline collapses each pair into its single stroke form.
Things that catch people out
- Lowercasing generated HTML turns every double arrow into a single one. Character references must be left alone by any case normalisation.
- Implication is one directional. Writing it where equivalence is meant, or the reverse, changes what a specification requires.
- Font coverage for double arrows is thinner than for single ones in decorative display faces, so a heading may fall back to a different family for that one glyph.
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HTML Entity Reference
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152 entities across 9 categories
Commonly Used
→Arrows(13)
±Math(35)
$Currency(8)
…Punctuation(21)
©Symbols(24)
πGreek(30)
½Fractions(6)
●Geometric(7)
æLatin Special(8)
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Related HTML entities
All html entities →Right arrow (→) in HTML
The rightwards arrow at U+2192, its entity forms, using it in a call to action without confusing a screen reader, and how it behaves in right to left text.
Left arrow (←) in HTML
The leftwards arrow at U+2190, its entity forms, why a back link needs a real destination, and the direction problem in right to left interfaces.
Mathematical operator entities: sets, logic and calculus
Named entities for summation, integral, partial differential, set membership, union, intersection and the logical connectives, with their code points.
Diagonal arrows: north east, south east and neighbours
The four diagonal arrows at U+2196 to U+2199, their numeric references, the external link convention, and why they have no named HTML entities.
Alpha (α) in HTML
The Greek letter alpha at U+0391 and U+03B1, its entity forms, its meanings in transparency and statistics, and the Latin A it is indistinguishable from.
Beta (β) in HTML
The Greek letter beta at U+0392 and U+03B2, its entity forms, its meanings in regression and finance, and the German eszett it is mistaken for.
Tools for this
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