And that is the wrong attitude to take. In some cases, the rules explicitly state what your options are. They do not actively forbid every other option, but that doesn't mean that other options exist. For example, the rules state there's 2 ways for Adepts to get Power Points after chargen. That doesn't mean a third method exists. They state a list of Called Shots, and unless you houserule other Called Shots they do not exist. They state the types of cover, you can't argue "it doesn't say this kind of cover wouldn't give me a -6 so clearly it does".
That said, there are indeed cases where if the rules don't actively forbid something it is generally allowed, but that often comes from a list forbidding things. For example, the rules state Summoned&Bound Spirits do not have Edge available. This means that any not-currently-Summoned/Bound Spirit has Edge available and is capable of using it.
If the rules state what the options are, those are the options. If they state what isn't allowed, you use common sense to determine what is allowed. If the rules use a phrase that common sense tells you has a specific meaning, unless official clarification or other segments of the rules make clear that isn't what it means, that will be what it means.
So short summary: If the rules explicitly state your options, other options are not allowed by default. If they do not, only then will your group-member's opinion be correct, albeit by GM fiat.
Random example: In SR4, one quality let you take something "for free". Common sense says free means no nuyen costs. Someone argued that this means no Essence Cost either, because it's labelled a Cost and the rules did not explicitly state it wasn't included. To him, free meant "no costs of any type", whereas to most free means "no monetary cost". The rules did not state it would not cost Essence, but common sense did.