When a poet writes in iambic pentameters, the length of the lines is determined by the form chosen to a significant extent. In free verse, the length of the lines is. It has been claimed by various authors that a line of metrical poetry is limited in its upper length by working memory capacity. This claim. tend to agree with her conceptually about the meter and line length, but many do not. Below is a poem that strays from isosyllabic lines and.