Is it important to you to have a key? A fair amount of 20th century music tried to scrupulously avoid a "key".
I did not know that! That is very reassuring. And I will stop worrying about what Key that song is in.
Your reply triggered a couple of other thoughts.
I knew about the trick of looking at the last chord - but it doesn't always seem to work. . . .
. . . Last week someone kept insisting that I ought to be ending a different song (another one that I have written) with the Chorus not a Verse. I kept saying, "But it doesn't work - it doesn't sound right.". I had not thought about why it did not work until now: the problem in that case is that ending on the Chorus would make the last chord an [E7] rather than a [C] and the song is in the Key of C.
Thinking about that incident made me wonder if people making their own arrangement to cover a song sometimes change the ending from a verse to a chorus, or vice versa, perhaps for "completeness" as in the case of my critic or perhaps to shorten a song? If so, then that might account for some of the times that the "last chord" clue is a red herring?
For the last year I have been writing songs with a friend who has a much better understanding of music theory than I do. (Typically, he produces all sorts of lovely chord progressions on the guitar and I then simplify the arrangement to within an inch of its life so that I can actually play it on a ukulele.) When he is the one starting off a new song, he might not begin by deciding on a Key but he usually settles on one quite quickly, as it helps him to explore chord progressions beyond the obvious ones (major, minor and diminished) that are likely to "work", where and how to step out of key, etc. Me, I remember about the major and minor chords, always forget about the diminished and the rest is still unexplored terrain!
I think I am at the stage of my ear being ahead of my understanding because I can find chords that "work" without knowing why they work. Where my friend also has the edge on me is that while I might hit on a chord that "works" he will often immediately recognise that it is a bit "weak" and will suggest a "stronger" alternative that works even better.
Having said all that, when I have written a song without knowing what Key it is in, the main problems in practice have been:
1) When I am putting together a set list then I like to make sure that I include songs in different keys for variety.
2) Communicating with others in "pub sessions" where it helps to shout out the Key of a song so others can join in playing more easily.
3) When creating a song sheet, deciding how to name chords that I have "found by ear" when there are several possible names for a particular chord shape. Knowing the Key helps me to choose a fitting chord name.
(There is whole other can of worms lurking in that last point. Writing songs on guitar and ukulele at the same time, or on guitar and then arranging for ukulele, often results in ukulele chords with implied roots; naming them according to the shape minus the implied root note results in some apparently whacky chord sequences. It can sometimes make the vocals sound a bit "off" when the melody was on the root note too - sometimes in a good way; sometimes not so good, so I change the melody.)
Thank you again for replying. I hope that something in my reply was interesting or helpful to you - or to anyone else stumbling across this question,
Play the Ukulele: The most fun you can have doing something badly!
"I'm not going to say I'm no Jim Morrison, I'm not going to say I'm no John Lennon - I'm not going to say I'm like The Monkees neither! - 'I'm a Believer!' - Some people say I make a pretty good musician - but I've always argued that's going to take me a long time . . . "
Wild Man Fischer