The words premise and premises are often confused, especially in the phrase on premises. Part of that confusion, I think, is that premises is the plural of premise, but it also has a different meaning that’s only seen in the plural form.
A premise is the basis of an argument or something that’s been assumed, and the plural form is premises:
- “The premise of Johnson’s theory…”
- “The unstated premises of his conclusion…”
Premises originally referred to a part of a deed, but it’s come to refer to a building, home, or place of business, or land with buildings on it. With this meaning, it’s always plural, even if it’s referring to a single building.
- “We moved from our on-premises datacenter to AWS.”
- “Consumption of alcohol on these premises is not allowed.”
Using premise to refer to a building or property in this sense is incorrect. I suppose if we’re talking about a server installed on a rooftop, using the data center as its base, we could call it an on-premise server. Otherwise, it’s on-premises.
- Premise @ Merriam-Webster Unabridged
- Premise @ Oxford English Dictionary
- Garner’s Modern English Usage, 5th ed., pg. 3483