How do note stems pointing in different directions help show polyphony?

In musical notation, the use of note stems pointing in different directions is a vital technique for notating polyphony, which is the simultaneous combination of independent melodic lines.1

By directing stems upward for one voice and downward for another, composers can clearly distinguish multiple melodic lines even when they are written on the same staff. This visual separation allows each individual voice to maintain its own distinct rhythm and melodic contour within a complex musical texture. This method of organization is essential for clarity in contrapuntal traditions, such as Renaissance motets and Baroque fugues, where several independent lines interact simultaneously.12