Music in the public domain

In Paul Turner's Blog by Paul Turner

Q: May this find you well and good.

I have a question with regards to hymns in public domain. I believe that you were in a choir some years ago, hence the enquiry.

My query is,  whether one can take a hymn in public domain and use its melody but substitute the lyrics. Is this an infringement somewhat? And vice versa? 

Thanks in advance for your help.

==

A: I’m not a lawyer, but my understanding is that music in the public domain is indeed in the public domain. You may use the melody with new lyrics and old lyrics with a new melody.