Actually there are more than two. But Ain't nobody got time for that. This is short and sweet...
The first approach to writing a song is the ever so banal: Lean To approach. Stick with the Nashville or blues formulas and 'lean' into those old, tried and three-chord tested patterns (i.e. *1,4,5 . I'm pretty convinced that this is the 'go to" approach for a majority of aspiring song writers, who have musical sensibility, but who also don t have a lot of trained imagination or understanding of the nuances (implemented by classicists and and post modern concerto, sonata and symphonic composers) . Writers in this category, tend to start "leaning" into what makes musical sense to them. Bound to scales without thought as to why they should deviate, And , while this isn't a horrible sin...the problem is; they 'follow' natural trail and get stuck in it. From that point on, they endeavor to search for next progression of phrases in a song by trying to conform to that trail, trying to match up with the their existing musical sensibility. By no means does it attest to any real creativity. And in such a predictable frame work, there isn't a lot of room for telling a rich story.
Push (Assertive) Approach: Surprisingly, this approach often does start off as a lean-to approach. It puts out the passive feelers to test the climate and cadence of the song's context. But, unlike the Lean-to approach, it doesn't stop there. There becomes a deliberate attempt to exact a musical *'propriety' for each phase and expression. (Often confused for the word 'originality'.) To achieve this, it must assert rather than propose and follow into a sensible pattern. Another way to state this is that this approach 'dictates' and drives a more interesting outcome of the song. ( This is the true essence of song-smithing...pounding out all the rocks for the gemstone that expresses exactly how you want it to express) Instead of a 1, 4, 5 an author may variate and create 1,4, 1,7, 1 If you try this variable sequence, you might recognize that its main verse structure of Hard Days Night (in key of E)
Fundamentally speaking; its not hard to use the push approach... ... In fact it might be easier, since the objective is usually NOT to conform to standard formulas. However, the artist would still typically want to sustain musical sensibility throughout the work. Music sensibility does not mean that the work must always be consonant' It can include dissonant tone and progressions (Hence, just look at our thriving Jazz communities ) Optimally speaking, an interesting song is more likely to use the
best of both approaches. (After all we gotta make donuts and they gotta be sweet, right?)
* 1, 4, 5 is music short-hand to describe the first, fourth, fifth note/chord in a given scale of a given key (example: 1,4,5, in key of E-major is notes/chord: E f g A,B).Most common in Blues.
*Musical Propriety: A term I use to describe the most sensible tact that a music phrase could exude in a given song. There are just some songs that say something so spot on, that its impossible to find a better way to express it. It is by definition; the arrival to (or closest to) absolute music sensibility.
Everything you just read, is merely my own perspective... What' s your perspective?... Holler back!