Formal, Verse, Prose
You probably noticed that the language in Richard III is pretty formal. This has a lot to do with the fact that much of the play is written in verse (mostly iambic pentameter), and characters' speeches tend to be carefully constructed.
Iambic Pentameter (The Nobles)
Let's talk about iambic pentameter, a type of verse that tends to be spoken by the nobility in Shakespeare's plays. Don't let the fancy name intimidate you – it's really pretty simple once you get the hang of it.
An "iamb" is an unaccented syllable followed by an accented one. "Penta" means "five," and "meter" refers to a regular rhythmic pattern. So "iambic pentameter" is a kind of rhythmic pattern that consist of five iambs per line. It's the most common rhythm in English poetry and sounds like five heartbeats:
da DUM, da DUM, da DUM, da DUM, da DUM.
Let's try it out on the second line of the play, taken from Richard's famous "Now is the winter of our discontent" speech:
made GLORious SUMMer BY this SON of YORK
Every second syllable is accented (stressed), so this is classic iambic pentameter. (Note: The word "glorious" is pronounced "glor-yus," which has just two syllables.)
Prose
Not every line in the play is verse. The lower-class characters, like the two murderers and the citizens, mostly speak in prose, just like we talk every day. Prose is less formal than verse, so it's befitting of their "low" social status.
For example, when the two murderers show up at the Tower of London to kill Clarence, they speak a lot of plain old prose, which is fitting because they're two "lowly" slime balls. Check it out:
Ho! who's here?
Yep, that's as plain as it gets.