A ligature is a unique pairing of two (or three) letters that become one glyph for no other reason, than it makes print design more beautiful. A Diphthong is the pairing of two vowels in any spoken language that form a new sound.
I love that pairings are often greater than the sum of the whole. My wife and I are exponentially better together than we ever were individually. It amazes me that God thinks the same thing about me and Him.