Great question … First you need to define what you call “knowing how to play”: Is it knowing how to play several known titles with your instrument, knowing how to release notes / chords from it without knowing any songs or mastering it to the point of playing any song by ear?
As a future composer, the only instrument you should know the best is the one that allows you to compose (DAW software, music writing software, duo pen / score book, etc …). The composition software often allows you to compose with samples of real instruments and in this case knowing how to play an instrument is not really useful to start. In addition, some music genres may be based primarily on software synthesizers.
But I still advise to touch at least one instrument as long as you can play notes or chords on it and chained them even clumsily. The goal here is to find your melodic phrases with this one. That said, nothing prevents you from learning to master the instrument.
Also, knowing several instruments will give you more possibilities in terms of composition. If I had to advise you one, it would be the piano or master keyboard of minimum 49 keys to begin because you can play a melody and accompaniment at the same time with your both hands. Make sure to have a USB / midi output to be able to record your playing directly on your composition software.
Personally, I have a digital piano, a guitar and a harmonica. I do not master them at all. For example, I will be unable to make a guitar buff with other guitarists. That does not stop me from using them to compose. On the contrary, switching from one instrument to another offers me other possibilities to compose and dozens of ideas. Which is very precious during your creative session.
I hope this article will be useful for you. Leave me a message in the comments if you liked it, if you have any comments or if you have questions or topics that you would like me to address.
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