What you probably know:
Somewhere in Latin class, you likely came across the most common irregular imperatives: dīc, fer, dūc, fac — Speak, Carry, Lead, Do. I repeat them in this order to recreate the mnemonic DFDF, SCLD — Dufus! Dufus! Scold him!, which I was introduced to early on.
What you might not know is whether these irregular forms are maintained within compounds. Indeed, they are, with one exception.
- Cōnfer haec exempla: compare these examples.
- Infer tribūtum reditūs foederāle semel in annō: pay your federal income taxes once a year.
- Eam addūc ut moveat: persuade her to move.
- Dēdūc maiōrīs verbīs fābulam: expand on your story with more words.
- Maledīc donec potes: curse them while you still can.
The exception is therefore fac, which is derived from faciō, a verb that more often than not takes its compounds in –ficiō. Such compounds do not display an irregular imperative.
- Effice tria carmina: complete three poems.
- Infice regem priusquam cīvēs cōnficiat: poison the kill before he kills the citizens.
If you’d like a refresher on the plurals: cōnferte, addūcite, maledīcite, facīte, efficite, etc.
Also, note that early late features the occasional face, dūce, and dīce (but never fere).
The Essential A & G: 182.