This is from a song lyric

> If a picture paints a thousand words,  
Then why can't I paint you?   
The words will never show the you I've come to know.  
If a face could launch a thousand ships,  
Then where am I to go?  
There's no one home but you,  
You're all that's left me too.  
And when my love for life is running dry,  
You come and pour yourself on me.

First the singer says *If a picture paints a thousand words*.

Followed by, *If a face could launch a thousand ships*.

Why does the singer sing "If a face could launch a thousand ships"?

Why not, "If a face can launch a thousand ships"?

Why is  _can_ used in the past?