B Major
0 - 4 - 7Root + major 3rd + perfect 5th
About B Major
B major is the barre chord guitarists avoid. It has five sharps, sits at the second fret where the strings still fight back, and offers no open-string version at all. Most players substitute it — with B7, with a capo, with a different key — and that avoidance is itself part of the chord’s story.
The notes
B, D♯, F♯ — root, major third, perfect fifth. Two of the three are sharps, which is the clue: B major is deep in the sharp side of the key system, five sharps in its own key, and none of its notes fall on an open string.
Lower the D♯ to D and the chord becomes B minor — easier, more common, and the version most guitar songs actually use. The major form appears mainly as a dominant, on its way somewhere else.
Why B7 is played instead
B7 in first position needs four fingers but no barre, and it does the same harmonic job in most songs: leading to E. That substitution is so widespread that many players know B7 for years before learning plain B.
When the full chord is needed, the A-shape barre at the second fret is standard. The alternative — E-shape barre at the seventh — is easier to hold and sits higher, which suits arrangements where the bass is covered elsewhere.
Where it shows up
B major is the V of E major, and that is where nearly every guitar encounter with it happens: E is a natural guitar key, and its dominant is not. The tension between those two facts is why B7 exists in so many songs.
As a tonic it is rare on guitar and common on brass instruments, where sharp keys sit comfortably. A song in B major usually did not begin on this instrument.