LEFT JOIN to a table using 2 keys from different tables

[David Perron]

Is there a way to do this?  Im trying to LEFT JOIN to a table that needs to
select based on 2 keys, but the query Im writing only has the keys
individually in two separate tables, like this.
The documentation shows how to do this when you are using 2 keys from both
tables, but not 1 key from 1 table and another key from another table
combined.
http://www.mysql.com/doc/en/JOIN.html

SELECT
FROM
        t1,
INNER JOIN t2 on (c1)
INNER JOIN t3 on (c2)
LEFT JOIN t4 on (c1,c2)

Thanks!