Well, I can see the confusion.
In musical theory, a perfect fourth is the interval equal to 5 half-steps, whereas a perfect fifth is the interval equal to 7 half-steps.
That's why we say that the bass guitar is tuned in fourths.
If you'd like to learn more, I suggest you follow
TapyTap's advise.
Here's a link that will do the job:
http://www.studybass.com/lessons/intervals/basic-intervals
And, if you ever have the time to study some more, take a look at StudyBass's other lessons.
They certainly helped me as a beginner, and I believe they'll be useful to you too.
But you look at the "Circle of Fifths" starting at "C" going clockwise you got C - G - D - A - E - B - Gb /F# - Db/C# - Ab/G# - Eb - Bb - F and then back to C.
I believe that the Circle of fifths to be the foundation of music chord progressions.
I have been playing music for more than 30 years. Not bass but Sax. The same rules apply whatever instrument.
Since I posted this about 30 minutes before, I looked at Study Bass, not a lot there. I then checked out Wikipedia, I found out that we all are basically
on the same road just looking at different scenery. Well so to speak.
If we check out the perfect fourth, vs. perfect fifth, I believe that we are talking about chord structures.
We can all agree chords usually in a basic chord goes: 1,3,5,7,9.
A "C" chord is C,E,G,B, & D.
I believe that if we follow Half step intervals we would get the seven Half Steps for the Perfect 5th. If we look at a fourth, we get 5 half steps.
But I think if we look at the chord and "proper scale" we would find a different story.
lets look at the basic triad 1, 3, 5
A major chord consists of the structure (using C major as my example) C, E, G.
If we look at the basic structure of a scale in any key you get the intervals W W H W W W H
(The W = Whole step
The H = Half step)
C D E F G A B C
w w h w w w h (<= these are intervals between each note)
So therefore a fifth to tonic of C would be G.
If we count the root as 1.
I am not genius but I know we still have to contend with the 12 keys and not so easy key signatures. We also get the luxury of dealing with Major, Minors and Augmented, diminished, and 7th chords. This is what makes music fun.
I hope maybe this will help someone as well.
All this being said, what is the tuning for a 5 string bass in perfect 5th's?