So (word)

So is an English word that, apart from its other uses, has become increasingly popular in recent years as a coordinating conjunctive opening word in a sentence. This device is particularly used when answering questions although the questioner may also use the device. So may also be used to end sentences. When ending a sentence, it may be:

a coordinating conjunctive to refer backwards to something previously mentioned
a coordinating conjunctive dangling "so" (sometimes called trailing "so")^[1] to refer forwards to something that may be said
an intensifying adverb.

Sentence opener

The first known written use of so as a sentence opener is in several lines of Chaucer's Troilus and Criseyde, published in the mid-1380s, for example:^[2]^[3]

So graunte hem sone out of this world to pace (So grant him soon out of this world to pass);

So as a sentence opener has been used in later historical literary works such as:^[2]

The Rape of Lucrece, 1594, by William Shakespeare
Pamela: or, Virtue Rewarded, 1740, by Samuel Richardson

It is widely believed that the recent ascendancy of so as a sentence opener began in Silicon Valley. Michael Lewis, in his book The New New Thing, published in 1999, noted that "When a computer programmer answers a question, he often begins with the word 'so.'" Microsoft employees have long argued that the "so" boom began with them.^[2]^[3]^[4]

Purpose

Various suggestions have been made as to its purpose:

as a coordinating conjunctive to refer backwards to something previously mentioned
as a discourse marker^[5]^[6]
to signal that the following words are chosen for their relevance to the listener^[7]
to provide a small amount of extra thinking time^[8]

In his Modern English translation of Beowulf, Irish poet Seamus Heaney uses "So" to translate the single-word opening line, Hwæt! (also rendered 'lo', 'hark', 'listen', etc). He explains that "in Hiberno-English Scullion-speak [...] 'so' operates as an expression that obliterates all previous discourse and narrative, and at the same time functions as an exclamation calling for immediate attention. So, 'so' it was".^[9]

Sentence closer

Referring back

"So" may refer back to something previously mentioned, such as:^[10]

"If she notices, she never says so."
Speaker 1: "Has somebody called an ambulance?" Speaker 2: "I believe so."

Other possibilities include:

"Absolutely so."
"How so?"
"I am afraid so."
"Indeed so."
"It is not so."
"It is so."
"Is it so?"
"Is that so?"
"...just so."
"...less so."
"Let it be so."
"...like so."
"...made it so."
"...make it so."
"...more so."
"Not so."
"...or so."
"Quite so."
"So?"
"...so-and-so."
"Why so?"

Dangling so

A dangling "so" in conversation invites the listener to articulate or consider the implications of the information provided without the speaker having to articulate it himself or herself.^[11]^[12] It has been interpreted as sometimes a form of bragging.^[13] A dangling "so" in conversation may be represented in text as "so" followed by an ellipsis: "...".^[1]^[14] Examples of dangling "so":

"Yeah, it's pretty exciting, though we're not really sure whether it will work out, so..."
Speaker 1: "How was your date?" Speaker 2: "Well, he didn't show up, so..."

Intensifying adverb

"So" may close a sentence as an intensifying adverb, such as in "I love her so". "So" in the middle of a sentence can also be an intensifying adverb, such as in "I so love her".^[14]

References

^ ^a ^b So What? What it means when people leave the word “so” dangling at the end of a sentence The Atlantic Julie Beck 26 Aug 2015
^ ^a ^b ^c Melissa (23 September 2015). "So, When Did We Start Introducing Sentences with So?". Today I Found Out. Retrieved 7 August 2017.
^ ^a ^b Anand Giridharadas (21 May 2010). "Follow My Logic? A Connective Word Takes the Lead". The New York Times.
^ Origins of using "so" as a sentence opener Boing Boing Mark Frauenfelder 17 June 2010
^ Goldberg, Haley (14 February 2014). "So… why is everyone saying "so?"". USA Today.
^ Bolden, Galina B. (2009). "Implementing incipient actions: The discourse marker 'so' in English conversation". Journal of Pragmatics. 41 (5): 974–998. doi:10.1016/j.pragma.2008.10.004.
^ "Do you use "so" to manage conversations?". Dictionary.com. 9 August 2013.
^ Mason, Mark (5 November 2011). "It's so annoying. So why do people feel compelled to start every sentence with 'so'?". The Spectator.
^ Seamus Heaney (19 February 2009). Beowulf. Faber & Faber. ISBN 978-0-571-25072-1.
^ Oxford Dictionaries
^ So… why is everyone saying “so?" USA Today Haley Goldberg 14 Feb 2014
^ It's Okay To End Your Sentences With 'But' Or 'So,' Right? The Huffington Post 15 May 2014 Claire Fallon
^ People who end sentences with 'so': Yes, they're bragging Crain's Chicago Business Lisa Bertagnoli 15 May 2010
^ ^a ^b Why do people end sentences with “so”? What effect does it have on conversation? Dictionary.com Jane Solomon 21 Aug 2013