[majewsky]

Things like "By doing X you agree to Y" are actually legally valid in some circumstances. The legal term is "implied-in-fact contracts": https://en.wikipedia.org/wiki/Implied-in-fact_contract

For example, that's why a railway operator (a private company) can fine you when you cannot present a valid ticket. When you get on the train, this action creates a transportation contract between you and the railway operator.

[belorn]

Contract law is a large and complex area of legal code, but the key term that get repeated is the "meeting of minds" which is the core disagreement between those that find EULA valid and those that find them invalid. Classical contract law holds that you can not make contract binding if one party has not read it or do not understand if for one reason or an other. This is used as the example when someone talk about switching a contract under the table, using microscopic hidden text, or other contract schemes. By using excessive length, language, complexity, and a position of power (you may not use the property you bought unless you agree to this additional arbitrarily terms) many see it as identical to switching the contract under table.

There is also some additional fun extras in contract law, like the concept of fair terms. This very old idea is that a contract should be a balanced deal. Terms that unfairly give one party undue benefits can then be challenged as invalid.

[kemitchell]

> There is also some additional fun extras in contract law, like the concept of fair terms. This very old idea is that a contract should be a balanced deal. Terms that unfairly give one party undue benefits can then be challenged as invalid.

US and state laws have a concept of "unconscionability" for extreme cases, as well as prohibitions on penalties, as opposed to prior agreements to fix damages based on reasonable estimates, and so on. But "the deal wasn't fair" isn't any general defense against breach of contract claims. Courts generally avoid digging into the business or other advisability of contracts. They err on the side of giving parties the deals they agreed to.

Perhaps you were speaking from the perspective of a different jurisdiction?

[bloak]

In some, but very few circumstances. In particular, I don't think the railway operator example works in the UK, at least not automatically, because, otherwise, why would they have special legislation relating to "penalty fares"? Look for the legislation on http://www.legislation.gov.uk/ if you're interested.

Here's an illustrative example that may or may not accurately correspond to the current state of the law in any particular jurisdiction, but it show why this implied contract stuff doesn't work in practice.

A farmer might put up a big notice saying: "By camping overnight on this field you agree to pay me £100 per vehicle per night." Then a bunch of travellers might camp there. Can the farmer sue the travellers for the £100 per vehicle per night? My guess is that he could only sue them for damaging his grass, because, despite what the notice said, the travellers didn't "agree"; they camped illegally and without permission, like they usually do. Probably they smashed up the notice to show what they thought of it. Therefore the farmer can only sue them for trespassing, not for breach of contract. (He might also sue them for the cost of replacing the notice if they did smash it up!)

Likewise, you could put a notice on the front door and every window of your house saying that by breaking into the house burglars agree to pay you X pounds. Would it help you in any way? Of course it wouldn't. You'd get laughed out of court if you tried it.