Would you, if you could?

A conditional usually consists of 2 clauses known as the main clause and the conditional clause.

The conditional clause usually begins with words like if or unless:

{conditional clause}, + {main clause}

if you leave me now, + you will take away the biggest part of me

If my heart had windows, + you’d see a heart full of love just for you.

Alternatively the two clauses can be reversed:

{main clause} + {conditional clause}

It’s no good + unless they love you all the way.

You’d still be mine + if I could turn, turn back the hands of time.

Note that we use a comma between the clauses when the conditional clause comes first, but we don’t tend to use a comma if it comes second.

Conditional Clauses Joined with ‘then’

If the conditional clause comes first, we can optionally add then. All of these are fine:

{conditional clause}, + [then] + {main clause}

if you leave me now, + then + you will take away the biggest part of me
if you leave me now, + you will take away the biggest part of me

If my heart had windows, + then + you’d see a heart full of love just for you.
If my heart had windows, + you’d see a heart full of love just for you.

Grammatically speaking the use of then is entirely optional and conditionals with or without it are perfectly fine.

To reiterate, if you use then, you must use if only when the conditional clause comes first:

If the conditional clause comes first, then you can use it.

You can use it if the conditional clause comes first.
*Then you can use it if the conditional clause comes first.

* An asterisk at the beginning of a sentence, denotes an ungrammatical sentence.

Useful Links

Conditionals in English Grammar – a useful overview.