Left Outer Join creates Cartesian join

I created an SQL using a Left Join with resulted in a cartesian join as a result.
The format is

select 

a.col1, a.col2, b.col1, b.col1, b.col3, b.col4 

from tablea a 

left outer join tableb b on b.col4 and b.col1 

where b.col5 < current_date()

The erroneously placed and (should be an = ) creates a cartesian join. Some other database technology calls a parser error on this.
In the case of the system, it happened in on column in the join condition is a primary key and the other is the lead column of a multi-column index of a primary key