2 for Slow, 4 for Fast
I have always tried to figure out how to write songs easily. I studied music theory, learned how to play hundreds of songs and composed about 20 of my own. As I was summing up my knowledge I saw the pattern of how my musical intuition works. I noticed that as I was playing two chords of every song that I've ever played my brain was always filling in the blanks and guiding me in what direction the song should progress. It's truly amazing how the song is right there after you have strummed just two chords. I'm not saying that everyone experiences it exactly the same way as I do, but for me, it works like that.
After I analyzed my experience a little further I came up with what I call the golden rule of songwriting:
2 chords for a slow song and 4 chords for a fast one -- that's all you need to have to know what the song will be like in its entirety.
Here are some examples. I just play F#m followed by E with the 6/8 rhythm and automatically (the people who have heard this timeless classic, of course) it's clear what song I'm playing. Or, for example, if I play am dm E am D C E, you realize that this is the theme song from the movie Le Jouet. I chose these songs because they have the most recognizable and clear-cut melodies that I've heard. These are the songs that I personally would be proud of if I wrote them myself because in my opinion, they represent the pinnacle of songwriting.