Most Helpful Guy
Not sure what you're asking. Somehow, I don't even think you're sure about what you're asking.
When you're the original tenant, the person who executes a lease directly with the landlord, you have the full leasehold interest on that property. You have what's called "privity of estate." You are in privy directly with the landlord. You owe rent directly to him, and he owes duties directly to you. If something is broken, if someone gets hurt in the property, etc., you can call him and he has a duty to investigate and maybe even repair or compensate.
When you're not the original tenant, but only a subtenant, you do not derive your "right" to possess or use the property directly from the landlord. Thus, you do not have "privity of estate" with the landlord. If someone gets hurt, or if something needs repairs, and you call up the landlord, he can actually completely ignore you. The "right" to possess and use your property is instead derived from the original tenant - someone with "privity of estate" with the landlord.
As a subtenant, your "right" to use the apartment is derived solely from the original tenant, and so, you only have "privity of contract" between yourself (the subtenant) and the original tenant. That means, contract law, not property law, governs and protects your relationship and right to use the property. If something needs repairs, or if someone gets hurt, or if the apartment falls into an unhealthy state of dispair, your only remedy is to go after and bother the original tenant. If the original tenant doesn't answer, you cannot sue him under a property theory like "breach of the warranty of habitability" or "constructive eviction," etc. You can only get money damages from the original tenant under a breach of contract theory, which is not really a great remedy because original tenants don't usually have deep pockets.
Here is where it gets interesting, and risky for you. Suppose you're an original tenant, and you have "privity of estate" directly with the landlord. Now, suppose the landlord "evicts" or "terminates the lease" of one of your co-tenants. Do you still have any "right" to be in that apartment? Yes! Your right is derived from the landlord, who owns the land, and he hasn't terminated "your" privity of estate. What if you're not the original tenant but only a subtenant, and have only "privity of contract" with the original tenant? Well, once the landlord "evicts" or "terminates the lease" of the original tenant, or the original tenant simply "surrenders" his lease to the landlord, the original tenant no longer has a "right" to use the apartment. And, since your right to use the apartment is derived from the original tenant's right to use the apartment, you now also no longer have the "right" to use the apartment. So, your housing status isn't really within your control.