FTP, name this rule which states that a hydrogen ion in a protic reagent will attach itself to the carbon atom with the most pre-attached hydrogen atoms.
The namesake of this principle first observed it in hydrohalogenation, but it has also been observed with hypohalous addition and acid catalyzed hydration, and it has been seen to result in a particular regioselectivity.  Its success lies in the intermediate created by the use of pi electrons from a double bond, and its explanation depends on recognizing the different stabilities of the two possible carbocations formed during protonation of the alkene.  FTP, name this rule which states that a hydrogen ion in a protic reagent will attach itself to the carbon atom with the most pre-attached hydrogen atoms.
The namesake of this principle first observed it in hydrohalogenation, but it has also been observed with hypohalous addition and acid catalyzed hydration, and it has been seen to result in a particular regioselectivity.  
Markovnikov's rule