https://saidtorts.lawbooks.cali.org/chapter/trespass-to-chattels-and-conversion/
Chapter 12 Trespass to Chattels and Conversion
Elements of Trespass to Chattels
1.​ Intent
2.​ To use or intermeddle with the chattel of another or to dispossess
the other of their chattel
3.​ Without permission or justification, and which
4.​ Causes harm to or destruction of the chattel or causes a substantial
interference with the possessor’s use of the chattel
Elements of Conversion
1.​ Intent
2.​ To exercise dominion or control over a chattel
3.​ Which dispossesses or deprives its owner permanently or
indefinitely
“Chattels” means “personal property” (as opposed to “real property” like
land or intellectual property like patents, copyright or trademarks).
Chattels include animals: the law treats pets as well as livestock as
chattels. Chattels do not include cash; generally, chattels are “things.”
The trespass in the tort’s name refers to the intentional use of another’s
chattel or interference without permission or justification for the use or
interference, resulting in destruction or demonstrable harm. The tort of
conversion conceptualizes the harm more broadly: it is the ownership
interest that has been violated because the defendant has “exercised
control” over the plaintiff’s property.
The tort of trespass to chattels is somewhat similar to the interest we
protect through battery: a right to be free from physical invasions, except
the interest here is narrower. Recall that battery did not require proof of
harm and even a “beneficial” invasion could be a battery if unconsented.
The interest protected through battery was the inviolability of the body.
Similarly, the interest protected through the tort of trespass to land is the
inviolability of the ownership of land. Conversion is more similar to
battery and trespass to land in that protects a broader interest than mere
harm to stuff: it protects the inviolability of one’s ownership right.
Consequently, a plaintiff who can show that their ownership right has
been interfered with in the defendant’s exercising control over the
plaintiff’s chattel will not have to prove harm. Just as was the case with
battery, making out the elements proves the invasion of the interest and it
is the invasion of the interest that constitutes the harm.
The intent required for both of these personal property torts is similar to
the intent for battery: simply using or “interfering” with the chattel, even
without any knowledge that one is interfering with another’s possessory
interest, is enough; specific intent to invade another’s interest is not
necessary. (Distinguish this from false imprisonment, which requires the
specific intent to confine.) The trespassory use must be substantial; it
would trivialize the judicial system if mere annoyances over objects of
common use were litigable.
Trespass to chattels is sometimes helpful in pursuing a claim for another’s
intentionally harming one’s animals. However, when serious damage to
personal property, including animals, occurs, the tort of conversion is the
usually the more appropriate action to bring and as a matter of practice,
the two torts are often brought together as alternative theories of liability.
While conversion requires a higher showing with regard to the
defendant’s conduct, if the plaintiff can successfully plead it, the plaintiff
need not prove harm. By contrast, to succeed in an action for trespass to
chattels, the plaintiff must prove the alleged harm or destruction to the
chattels. Note that causing the value of the chattel to drop counts as
“harm” to the chattel. The plaintiff can recover for all the harm to the
chattel and incidental damages the unauthorized use causes. The measure
of damages is the market value at the time of the dispossession or
intermeddling.
For example, if a person borrows their roommate’s car without permission
and returns it safely without damage, there has been no trespass to
chattels so long as the owner did not suffer as a result of not having it
available during the time of the roommate’s use. Trespass to chattels
would require that the driver harm the car or that the owner need the car
and be unable to use it during the specified time of the unauthorized use.
If the owner needed it for some purpose and had to take a cab instead of
driving, for instance, or missed an opportunity for a job interview, the
damages from the tort could compensate for those harms even if the car
was not damaged.