When the typewriter was introduced in the late 1800s, typists utilized two spaces between sentences to emulate the manner of conventional typesetters. While wide sentence spacing was phased out in the publishing business in the mid-twentieth century, it persisted on typewriters and, subsequently, computers. Today, most computer fonts include only one space as standard; those that don't can usually be configured to display two.
He argues that the practice of two spaces between sentences dates back to the days when everyone typed on manual typewriters. Because of how typewriters handled proportional spacing, typewritten manuscripts with two periods between sentences were simpler to read. This idea is supported by the fact that many early typewriter keyboards included a "period" key for inserting two dots every time you pressed the key.
Today, most lawyers use computer-generated documents. One space indicates that there is one sentence break in the text. Two spaces between sentences looks like overkill and can be interpreted as an indication that there are multiple breaks in the text. The practice of using two spaces instead of one came from typewriter manufacturers who wanted to encourage writers to use more reasonable spacing between sentences.
The two-space rule does not apply to all professions. In academic writing, where multiple paragraphs are allowed within a single sentence, only one space is used between sentences. A PhD student who types her dissertation up manually will often leave two spaces after each sentence as a reminder that there should be a break before starting the next one. However, this is done solely as a visual cue -- there is no rule requiring multiple spaces before a sentence break.
In legal drafting, where each paragraph represents a separate section of the document, two spaces indicate that there should be a separation between these sections.
Because the typewritten monospace typeface has so much more spacing, authors who used typewriters needed the extra space after punctuation to denote a complete stop, such as a period, question mark, or exclamation point. Using two spaces will cause your typeset to be distorted. This is why writers should never use double spaces after periods.
Hence the adoption of the two-space rule—on a typewriter, an extra space after a sentence makes the text easier to read. Because we've all switched to modern fonts, adding two spaces after a period no longer enhances readability, typographers say. It diminishes it.
But they still add the extra space anyway. And for good reason: Saves time!
The old rule - called "the last word rule" - was that you should not put a line break after the last word of a sentence unless there's more than one word on the line. So if "John loves Mary" had been written as one sentence, there would be no need to insert a line break because this would mean that "John" and "Mary" are on separate lines, which would make reading the sentence harder rather than easier.
However, this rule was never entirely accurate or useful; in fact, it can be very confusing at times. For example, if "John loves Mary" were written as two sentences, then a line break would be needed after both words, even though this would mean that "John" and "Mary" are on separate lines. This is why professional writers often recommend putting a blank line between each sentence, so that you don't end up with words that are too close together or difficult-to-read chunks of text.
Because the spacing between words on a typewriter was irregular, the extra space was required to define the beginning of a new phrase. If you didn't learn to type on a typewriter, you're probably using two spaces after the period because you're emulating the writing of someone who did. This is called "period punctuation."
In modern times, one space has replaced the other as our default setting for all types of writing, including print and web media. This single space can be typed as well as written with a blank key or the option button on most computer keyboards.
When you write a letter or an email, unless you specify otherwise, people will assume that you want your text formatted in standard English. So if you don't mark up your letters with some form of punctuation, they won't be considered complete sentences by the recipients. For example, if you send a letter from one person to another and there's no punctuation at all, then it's likely to be seen as an informal message rather than an actual sentence.
The use of periods, commas, semicolons, and colons to separate clauses in a sentence is known as "sentence punctuation". Punctuating a sentence helps readers understand the relationship between ideas within the text. Without these marks, readers would not know how many clauses make up a sentence or whether several sentences are part of one larger idea.
Monospaced type produces text that seems "loose" and uneven; there is a lot of white space between letters and phrases, making it more difficult to notice the gaps between sentences instantly. As a result, the two-space rule was adopted on a typewriter; an extra space following a sentence makes the text easier to read. This is known as "the pause rule".
In modern times, monospaced type is used in computer programs to show labels or commands within a document. These elements are referred to as "monospaced fonts", because each character takes up the same amount of space when printed or displayed.
The term "monospace" also describes a font in which all characters have the same width. This is in contrast to "proportional fonts", which vary in width according to the letter or figure being typed or drawn. Monospaced fonts are commonly used in programming because they make it easy to see where one command ends and the next begins.
When typing a manuscript, scientists use monospaced fonts so that their papers appear uniform and professional. Using a monospaced font ensures that paragraphs stay separated from each other, allowing readers to distinguish information across different sections of the paper.
People also add spaces between words when writing by hand. This is called "editing", and it makes documents clearer and easier to read. Without spacing, texts can look messy and confusing.