A commenter on the Madison / IP thread uses the intellectual property/tangible property analogy to argue for injunctions against infringement of intellectual property (apparently including infringement that doesn't interfere with the owner's use of the property), and goes on to say (in response to another commenter's argument),

[T]he analogy to trespass does not require an actual dimunition of your own use. It's 1L property law that a trespass is actionable even if nothing is broken, if you're not home, if your use of the property is not denied in any way. The offense is crossing the property line.

Now, the amount, impact, and circumstances of the trespass relate to damages, but liability starts from crossing the property line. There's not, nor has there been, a requirement that the property owner's actual use be diminished for there to be a trespass, as opposed to, say, conversion.

I can't say with confidence when injunctions should or should not be available in intellectual property cases; here, I just want to alert people to a common problem with analogies -- the simple problem that the analogized-to body of law is often more complex than the analogizer suggests.

For instance, let's assume that intellectual property is analogous in important ways to tangible property. There are (at least) two important classes of tangible property: real estate and personal property (also known as chattels, and generally just referring to all tangible property that is not real estate).

The "1L property law" rule to which the commenter refers is a rule applicable to real estate. But the rule for tangible property is different: As Restatement (Second) of Torts § 218 puts it,

The interest of a possessor of a chattel in its inviolability, unlike the similar interest of a possessor of land, is not given legal protection by an action for nominal damages for harmless intermeddlings with the chattel. In order that an actor who interferes with another's chattel may be liable, his conduct must affect some other and more important interest of the possessor. Therefore, one who intentionally intermeddles with another's chattel is subject to liability only if his intermeddling is harmful to the possessor's materially valuable interest in the physical condition, quality, or value of the chattel, or if the possessor is deprived of the use of the chattel for a substantial time, or some other legally protected interest of the possessor is affected as stated in Clause (c). Sufficient legal protection of the possessor's interest in the mere inviolability of his chattel is afforded by his privilege to use reasonable force to protect his possession against even harmless interference.

See also Intel Corp. v. Hamidi, 71 P.3d 296, 302 (Cal. Supreme Ct. 2003).

Now maybe the rule as to personal property is wrong. Or maybe intellectual property is more analogous to real estate than to personal property. Or maybe many (most? all? some?) infringements of intellectual property are like those infringements of personal property rights that do warrant an injunction. Or maybe the analogies aren't really helpful here, and we should support injunctions against infringements of intellectual property for other reasons.

But the one thing that should be clear is that, even to the extent the intellectual property / tangible property analogy is sound (and it certainly is an analogy that's long been recognized in many respects by the law), we have to recognize that the analogized-to category is not legally homogeneous. Before we apply by analogy "1L property law" rules relevant to one class of tangible property, we should acknowledge that there are other rules relevant to another class of tangible property, and explain why we are choosing one sort of rule and not the other.