In justified text, the spaces between words, and, to a lesser extent, between glyphs or letters (kerning), are stretched or sometimes compressed in order to make the text align with both the left and right margins. When using justification, it is customary to treat the last line of a paragraph separately by left or right aligning it, depending on the language direction. Lines in which the spaces have been stretched beyond their normal width are called loose lines, while those whose spaces have been compressed are called tight lines.
The following table displays the difference between a justified (flush left and flush right) and a flush left (and ragged right) text.
It was common for early electronic printers to use monospaced fonts, and word processing packages designed for these systems often allowed justified text to be simulated by randomly inserting extra spaces between words in the shorter lines. This is not generally considered good practice, as it leads to very uneven spaces between words.
justified (flush left, flush right)
Thy father was delighted and cried out to the servant, 'Give him a hundred and three gold pieces with a robe of honour!' The man obeyed his orders, and I awaited an auspicious moment, when I blooded him; and he did not baulk me; nay he thanked me and I was also thanked and praised by all present. When the blood-letting was over I had no power to keep silence and asked him, 'By God, O my lord, what made thee say to the servant, Give him an hundred and three dinars?'; and he answered, 'One dinar was for the astrological observation, another for thy pleasant conversation, the third for the phlebotomisation, and the remaining hundred and the dress were for thy verses in my commendation.'" "May God show small mercy to my father," exclaimed I, "for knowing the like of thee.
flush left, ragged right Thy father was delighted and cried out to the servant, 'Give him a hundred and three gold pieces with a robe of honour!' The man obeyed his orders, and I awaited an auspicious moment, when I blooded him; and he did not baulk me; nay he thanked me and I was also thanked and praised by all present. When the blood-letting was over I had no power to keep silence and asked him, 'By God, O my lord, what made thee say to the servant, Give him an hundred and three dinars?'; and he answered, 'One dinar was for the astrological observation, another for thy pleasant conversation, the third for the phlebotomisation, and the remaining hundred and the dress were for thy verses in my commendation.'" "May God show small mercy to my father," exclaimed I, "for knowing the like of thee.
The following paragraph has been justified by a monospaced text-processing system:
And indeed thou shalt never find a man better versed in affairs than I, and I am here standing on my feet to serve thee. I am not vexed with thee: why shouldest thou be vexed with me? But whatever happen I will bear patiently with thee in memory of the much kindness thy father shewed me." "By God," cried I, "O thou with tongue long as the tail of a jackass, thou persistest in pestering me with thy prate and thou becomest more longsome in thy long speeches, when all I want of thee is to shave my head and wend thy way!"
Justification sometimes leads to typographic anomalies. When the spaces between words line up approximately above one another in several loose lines, a distracting river of white space may appear. Rivers appear in right-aligned, left-aligned and centered settings too, but are more likely to flow in justified text due to extra word spacing. Another problem occurs when using justification in narrow columns, when exceptionally large spaces appear between only two or three words (called a loose line). Both of these problems are reduced by the addition of hyphenation. In WYSIWYG word processors, this is usually done manually, because the writer handles hyphenation on a case-by-case basis, whereas typesetting systems such as LaTeX perform automatic hyphenation, with manual override where required, because the writer cannot tell during text preparation where a line will end in the typeset output.
People with dyslexia (particularly Scotopic Sensitivity Syndrome) find that justification interferes with cognitive understanding. Since spacing after a full stop is only a fraction of the spacing within a sentence (like 1 to 10), full stops only marginally contribute to the river effect. Hyphenation can also be an issue.
Common word-processing software only adjusts the spacing between words, which is a main source of the problem. Professional publishing software significantly reduces the rivers effect through adjusting the spacing between characters as well as using more advanced digital typography techniques such as automatically choosing among different glyphs for the same character and slightly stretching or shrinking the character in order to better fill the line. The technique of glyph scaling or microtypography has been implemented by Adobe InDesign and more recent versions of pdfTeX.
The use of movable type solidified this preference from a technological point of view. It was much easier to handle and make emendations to large amounts of type that had words or syllables at the ends of lines than it was to respace the ends of lines.
Its use has only waned somewhat since the middle of the 20th century through the advocacy of the typographer Jan Tschichold's book Asymmetric Typography and the freer typographic treatment of the Bauhaus, Dada, and Russian constructivist movements.
Not all "flush left" settings in traditional typography were identical. In flush left text, words are separated on a line by the minimum word spacing built into the font.
Continuous casting typesetting systems such as the Linotype were able to reduce the jaggedness of the right-hand sides of adjacent lines of flush left composition by inserting self-adjusting space bands between words to evenly distribute white space, taking excessive space that would have occurred at the end of the line and redistributing it between words.
This feature, known as "ragged right" or "in and out ragged", was available in traditional dedicated typesetting systems but is absent from most if not all desktop publishing systems. Graphic designers and typesetters using desktop systems adjust word and letter spacing, or "tracking", on a manual line-by-line basis to achieve the same effect.