, and for the sake of argument 
(altho this is indeed a serious subject, and I like to use these posts to research and educate myself): I think you are unlikely to be prosecuted in Texas for shooting a drunk who turned the door knob and walked into your home at 2:00 a.m.It appears to me that the "Castle doctrine" as implemented in Texas law was to relieve the resident of a habitation from having to determine an intruder's intent. Trying to determine "intent" when someone unlawfully and with force enters the house puts the resident at a huge, and potentially fatal disadvantage. The resident is supposed to be there -- the intruder is not, and that is sufficient to tip the scales in favor of the resident presuming the worst and acting accordingly.
As Seamus noted, a self-defense justification requires "the actor reasonably believes the force is immediately necessary;" BUT "The actor's belief under Subsection (a)(2) that the deadly force was immediately necessary ... is presumed to be reasonable if ...the person against whom the deadly force was used...unlawfully and with force entered, or was attempting to enter unlawfully and with force..."
http://www.statutes.legis.state.tx.us/D ... m/PE.9.htm" onclick="window.open(this.href);return false;
No real requirement to determine if someone is applying for Charles Manson discipleship or is just the drunken frat kid from two doors down. If he opened the door and entered without permission, you are presumed to rationally believe deadly force is necessary to deal with him. (See big exception to the "permission" in last para below!)
As noted earlier, I tried looking up legal definitions of "force" to see what this actually meant. This does not seem to be codified in statute, but what I found were teaching examples used in law schools and police training materials, and they were fairly consistent with each other and the post I made above (with the quote from Mr. Cotton). "Force" can be as simple as pushing open a door. Breaking and splintering not required. Locks not required. I can't point to a case, but it would seem there are so many cases that this has pretty much been "codified" in teaching materials across the country. The legislators who enacted this Texas law understood it this way.
I think the example Seamus linked to of a homeowner being prosecuted for shooting an intruder does not counter any of this, because he is not being prosecuted for shooting an intruder in his house. According to the police a) the homeowner and the college kid did not encounter each other in the house, and b) the shooting took place off the property, in the street. This did not fall under the Castle Doctrine. And since the kid did not have any of the homeowner's property, nor confronted the homeowner or offered any threat out in the street, it doesn't fall under any other doctrine. Had the homeowner shot him in the house, I really don't think he would have any problem with the DA.
Now I don't recommend you blindly shoot at anyone moving around in your habitation or banging on the door without at least identifying that he is really not supposed to be there. There are too many stories of family members or house guests coming in late and getting shot. Also, there are people who can lawfully enter or attempt to enter your house with force, among them police and firefighters responding to emergencies. I have knocked on the wrong door more than once in the wee hours as a first responder, because the dispatched address was wrong, or the houses were not marked and we had to search around. (I always stand to the side when I knock). I have broken into houses when the party who called was not able to get to the door (we try to let the cops be the first one in the door to sort things out, but they are not always available). We don't like to do this, and it doesn't happen often, but it can, and police and firefighters can come to the wrong address too. "Be sure of your target and what lies behind it" is still a good rule at 2 a.m.
