Deductive reasoning goes from the general to the specific. Put another way , you start with no opinion and run things through a series of progressively smaller funnels and whatever falls out the bottom is the answer.

I don't know if this is what your looking for, but it sound like your describing "The Process of Elimination".

This doesn't necessarily work out: Sometimes, when dealing with a complicated problem, you don't know ALL of the possibilities; so even if you think you have eliminated all of the impossible answers, and are left with one which you can't disprove, there may still be other explanation(s) which are more accurate...and which may be more or less complicated.

I think the principal you are looking for is "Occam's razor" also spelled Ockham's razor. It originated in the 14th century. For more, check a search engine.

1) "Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth. Sir Arthur Conan Doyle in "A Scandal in Bohemia", spoken by the character Sherlock Holmes." Source and further information: http://en.wikiquote.org/wiki/Truth 2) "In logic, elimination refers to the rule of inference known as the disjunctive syllogism." Source and further information: http://en.wikipedia.org/wiki/Elimination "A disjunctive syllogism, historically known as modus tollendo ponens,[1] is a classically valid, simple argument form: A is B or C or D A is not C or D Therefore, A is B" "It is either red, green, yellow or blue. It is not green, yellow or blue. Therefore, it is red." Source and further information: http://en.wikipedia.org/wiki/Disjunctive_syllogism 3) "What is wrong with the Sherlock Holmes type deductive reasoning statement: If all of the possible hypotheses are eliminated except for one, then that hypothesis, no matter how unlikely, is the correct hypothesis? Because deductive reasoning draws conclusions with complete certainty, it is tempting to sometimes believe that we are using deductive reasoning when in fact we are using inductive reasoning. The fictional Sherlock Holmes makes this mistake. Rarely if ever, can our reasoning concerning nature be considered to be deductive reasoning. The problem with doing so is that this implies that all of the possible hypothesis can be identified, when in fact we may never know all of nature’s secrets. This is why it is so important to conduct experiments and collect field data to verify our logic. Through these experiments we often learn of nature’s secrets that are then added to our base of knowledge. Even though inductive reasoning does not draw conclusions with complete certainty, it is generally much more helpful than deductive reasoning. Inductive reasoning allows us to reach conclusions on what has not been directly observed based on what has been observed. It is inductive reasoning that allows geologists to use present observations to draw conclusions about events that happened million of years ago in the Earth’s distant past. More often it is inductive reasoning that allows us to use observation of the past to anticipate probable events of the future. For example, if every day a bus stops by a bench at 4:00 pm, and we are sitting on that bench a few minutes before four, we would be expecting a bus to arrive within a few minutes. Notice that while our inductive reasoning may be correct the vast majority of times it is still not guaranteed to always be true. No matter how consistent the bus may be, we can not say with complete certainty that the bus will be there tomorrow at the predicted time. When attempting to solve a problem we would like to consider all of the reasonable hypotheses. But to believe that we can identify all of the possibilities is often the equivalent to stating that we have limited imagination." Source and further information: http://dinosaurtheory.com/theory.html "That quote is actually a logical fallacy; it assume that you are aware of all the possible explanations. There may be an explanation which you simply haven't thought of yet, which is neither impossible or implausible." Source and further information: https://bbs.stardestroyer.net/viewtopic.php?f=5&t=125310 4) "‘If you’ve eliminated all other possibilities whatever remains must be the truth,’ is the famous a quote from the brilliant, but fictional, detective Sherlock Holmes. It seems to be an inescapable statement of cold, hard logic but it is often used in movies or on TV as a fig leaf to cover a huge leap of logic on the part of the hero or as justification for why the answer to the mystery at hand must be ghosts, aliens or some other supernatural phenomena. Is the statement a logic fallacy, a practical impossibility or a viable method of investigation that is being misused?" "The actual quote is this: “Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.” As stated this is an obvious point of logic - the truth must lie within the set of the possible, which is defined as everything that is not impossible. But Holmes (by which I me Sir Arthur Conan Doyle, the author of Sherlock Holmes) meant the statement as a practical rule of thumb. As an investigator you create a mental list of all potential explanations for a situation. You then systematically eliminate those explanations that you can demonstrate are impossible, either through logic or empirical evidence. Whatever you are left with is the solution - even if it may seem extremely improbable. Holmes, the hyper-rationalist, was a genius at just this type of endeavor. He could make the connections necessary to eliminate possibilities. He also had the imagination to consider possible solutions that may at first seem entirely improbable - but if that is what you are left with then it must be true. But Sherlock Holmes was working within a specific framework - a materialist, rational, scientific view of the world. Within that framework this process of elimination works well." "problems arise when this very logical principle of investigation are applied without constraints. The logic breaks down in a world where one allows for the existence of magic. How, then, does one define possible vs impossible? Holmes clearly assumes magic does not exist, and Doyle places him in a world (the real world) where magic in fact does not exist. Therefore Holmes (very much unlike Scully from The X-files, who lives in a paranormal world) is never “baffled” when his rational explanations do not fit an irrational world he refuses to accept." "So Sherlock Holmes’ principle needs to be clarified, in a way that was simply assumed by Holmes: Within the set of known phenomena, once you have eliminated the impossible, whatever remains, no matter how improbable, must be true. If the entire set of known phenomena are eliminated as impossible, then the solution is simply uknown until a new phenomena that can serve as a solution is positively established. That is a bit more cumbersome than Doyle’s poetic phrasing, but it is more complete. So before we can conclude that the earth is being visited by ET craft, we must completely eliminate all possible explanations (even the quirky and improbable ones) and then find evidence that points specifically to ET craft, rather than just assume that “unknown” means extraterrestrial." Source and further information: http://www.theskepticsguide.org/sgublog/?p=320

It's 'principle' in your case. An easy way to remember between principle and principal is, "Your principal is your pal."