Suivez ces instructions au pied de la lettre.
swee-vay say zaa-strewk-seeYAW oh peeYAID lah LET-truh. Click below to hear this.
Follow these instructions to the letter/exactly/precisely.
This is what you say when you are explaining something really, really important–say, how to handle explosives, or how to pack Great-Grandma’s priceless antique goblets for shipping.
True, you can also say Suivez ces instructions à la lettre. It literally means to the letter. That’s fine for less critical matters, such as washing a teddy bear or chopping up carrots. Really, who cares what shape the carrots end up, unless you are a prep chef in a high-end restaurant?
Au pied de la lettre literally means to the foot of the letter. Don’t alter a single letter, or even the foot of one. You might end up wrapping the package “micely” instead of “nicely”, which could be disturbing to some people. Or what if you read “DO NOT STACK” as “DO NOT SNACK”?
Yes, letters have feet, sometimes very graceful little feet, at least if they are in a serif font. Sans-serif have no feet, so they are irrelevant to this discussion. Designers often claim that serif fonts are easier to read, so if you really seek clarity in your life, use letters with feet and Suivez ces instructions au pied de la lettre.