# When to use \par and when \\

What is the difference between \par and \\ and when should I use \par instead of \\?

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Well, use \par when you want a new paragraph (and don't wan to insert a blank line for some reason, such as in macro/environment definitions), and use \\  in array and tabular. That's the rules I have been following. –  Peter Grill Nov 14 '12 at 0:57

\par is a TeX primitive and is the same as a blank line (except in special environments such as verbatim where the usual rules don't apply). It ends horizontal mode, causes TeX to break the horizontal text into lines placed on the current vertical list, and exercises the page breaker which may possibly cause the next page to be shipped out.

\\ is different in almost every respect. It is a macro not a primitive, and its definition changes wildly in almost every LaTeX definition. The definition in normal text, a center environment a flushleft environment and a table are all different.

In normal running text when it forces a linebreak it is essentially a shorthand for \newline this does not end horizontal mode or end the paragraph, it just inserts some glue and penalties at that point into the horizontal material so that when the paragraph does end a linebreak will occur at that point with the short line padded with white space.

You should rarely need to use \\ in documents apart from its use in alignments (where it is a macro based on the \cr primitive), and you should rarely need \par in documents as a blank line should suffice.

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a consequence of using \\ instead of paragraph breaks is that (la)tex continues to load text into memory, and doesn't actually output anything until an actual paragraph break occurs. this may not be so important now, with memory capacity being so large, but when memory was a much more scarce resource, failing to use paragraph breaks was a sure way to run out of memory and crash the job before it finished. it will still slow down the processing when the "paragraphs" are very long. –  barbara beeton May 2 '14 at 1:39

In text mode, \par starts a new paragraph, while \\ ends the current line.

So when to use each one?

\\ should be used with parsimony, when you want to break of the rhythm of your current argumentation, but without jumping to a new idea / argument (which would require starting a new paragraph).

\par should actually be used even less frequently. Not that you do not want to start new paragraphs (you do want to keep paragraphs to reasonable lengths!), but you should start new paragraphs by leaving an empty line in your TeX code. This has the exact same effect as using \par, but will make your code much more readable. \par is therefore mostly used when defining macros.

Note that outside of text mode, \par will usually lead to an error, while \\ usually works as expected to start a new line (like while in an tabular or array).

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\ in text usually works except when it says ! LaTeX Error: There's no line here to end. (e.g., dual \ to produce two blank lines in a paragraph ... there are more reliable ways to do that.) [gosh — don't understand where that –  wasteofspace Jan 12 at 20:04
the previous one by me showed my non-understanding of markdown (or whatever it is). i was trying to use backslashes, and the output was all to pot ... and in the allowed 5 minutes i couldn't sort the problem. must remember to keep my mouth shut in future... :-( –  wasteofspace Jan 15 at 10:13