I had to post an addendum to my article about “If…then” conditionals. There was a comment left (since deleted) arguing that writers should not drop the “then” as I had suggested. Two others came back agreeing with the commenter. One of the objections was about how the word “then” would benefit non-native English speakers. However, one German speaker came back saying the “then” wasn’t needed. I also did some linguistic research (Hindi and Chinese mostly) and learned that the order of clauses probably matters more.
Below is the comment I last posted. Unfortunately, all of the replies/comments got deleted when the original commenter withdrew her comment.
Any other comments?
Overall, the use of the word “then” is complicated. It doesn’t follow the same rules as other conjunctions. It’s also easily confused with “than.” (See http://grammar.ccc.commnet.edu/grammar/conjunctions.htm)
If you read your sentence out loud, first with the “then” in, and then without it, how does it sound?
You will probably find that the sentence with the word “then” will convey a more formal tone because it’s emphasizing what comes after. Sometimes that’s what you need so you can show how serious or dangerous the consequences of an action are. Example: “If you play with matches, then you’re going to get burned.”
The key point is that you should always put the “if” clause before the “then” clause. Based on some quick research on conditional statements in other languages, putting the “if” part first is the natural order across languages.
But, the very safest thing to do is create an “if…then” table.