A piano teacher used to speak often about articulation when talking about how to successfully meet the keys with the fingers. I understood it technically then, but now I also understand it as a matter of diction and communication. A sensibility of intent: that every keystroke should be intended and have an awareness that was meant from actual muscle action to brain and mind purpose interpreted on the path from mind to execution at the tip of a finger.
When a vocalist does this the experience, for the listener is effortless. It does not matter the era or age or influence, style, or even culture, because the soundscape is the communication. It is language and speech, dialect and pronunciation, but not just clarity of a word formed by the mouth, lips, and tongue — it is presentation and conversation; an artist says because they see, and the consumer hears and sees because of the artist.
Nat King Cole’s artistry makes you see and feel like you are seeing all over again. The communication is conversation, and that conversation is articulate.