Dividing by 2

Most of the time, when you are playing drums, the beat is going to be subdivided evenly into pairs of sounds, or pulses.  For example, you might be playing along with some guitarists and pulsing evenly on 1,2,3,4 and then subdivide the 2 and 4 beats into 1,2,and,3,4,and.  When the division is uneven, or if there is somehow an odd number of pulses, then the listeners might be distracted and you might lose the beat or the groove.  There are times, however, when the music calls for this, and if the other musicians expect it, or the song calls for it, then it works - irregular beats, jazz, hip-hop etc.  While learning the basics, stick with even, regular beats, until you teach your hands and limbs to keep a good steady time going.  Worry about the odd stuff after mastering the even stuff!