Short answer. It can change the contract itself. If you gave permission to use the thing, the arrangement stops being safekeeping and becomes a loan, unless safekeeping is still its main purpose. But permission is never assumed — whoever says you gave it has to prove it.
What the law says
When the depositary has permission to use the thing deposited, the contract loses the concept of a deposit and becomes a loan or commodatum, except where safekeeping is still the principal purpose of the contract. The permission shall not be presumed, and its existence must be proved.
Civil Code, Article 1978 — Permitted Use Converts the Deposit. Read the full provision →
What use does to the arrangement
Article 1978 states what happens when a keeper is allowed to use what he is holding: When the depositary has permission to use the thing deposited, the contract loses the concept of a deposit and becomes a loan or commodatum, except where safekeeping is still the principal purpose of the contract. The label on the receipt does not decide this. What decides it is why the thing changed hands. If it went across to be looked after, it stays a deposit. If it went across so the other person could use it, it has become a free loan of the thing — what the Code calls commodatum.
Permission is never assumed
The article closes with a protection for owners: The permission shall not be presumed, and its existence must be proved. The burden sits on the person claiming he was allowed. Handing over the keys with the car does not by itself permit him to drive it, and giving the papers with a machine does not permit him to run it. Nor does long silence amount to consent — that you never complained is evidence of something, but it is not the same as agreeing. Anyone who wants freedom to use the thing should ask in writing, and an owner who does not intend to give it should say so plainly.
Why the difference matters
The two arrangements carry different duties. A keeper's job is to preserve the thing and give it back. A borrower's is to use it for the agreed purpose and return it in due course, ordinary wear aside. Liability shifts as well: Article 1979 makes a keeper answer even for an accidental loss where he used the thing without permission or let others use it, so an unauthorised use can leave him carrying a fire or a collision that was nobody's fault. The exception matters too — where safekeeping remains the principal purpose, incidental use does not convert the contract.
If your property was used without permission
Write to the holder at once, say that no permission was given, and demand the thing back on a specific date. That letter often decides a later dispute, because delay in returning is itself a ground of liability. Record the condition of the item when you get it and keep evidence of what it was worth before. Damage caused, or income earned from it, are separate claims you may be able to pursue. If the arrangement was written, check whether it already says anything about use. Claims of this kind are subject to time limits, so take advice early.
Related provisions
- Civil Code, Article 1978 — Permitted Use Converts the Deposit
- Civil Code, Article 1979 — Liability for Fortuitous Loss