When we have spoken in the past about scales, we have used words like intervals, tones, semitones, flatted this, sharpened that, perhaps even diminished, augmented, and so on. But the simple truth is that ALL scales you will need in barbershop can also be identified by one of two just unique patterns for their notes.
Every major scale has the identical pattern of notes regardles of what it is called. eg C major, D major, F#major Db major etc all follow the same pattern.
The same applies to minor scales. They too will have their own unique pattern that will apply regardless of what it is called. C minor, D minor, F# minor, Db minor, are all built up using a unique minor pattern.
So in order to be able to work out the notes in all the major scales and all the minor scales, you only need to remember just two patterns.
So what are these patterns. Well the easiest way to explain is for you to visualise a keyboard.
If you then press any key, you will generate a note and if you then press the next key up, you will generate a different note a semitone higher. If you then press the next key up again, the note you produce will be a semitone higher from the previous note but a full Tone away from the first key you pressed.
The keys you pressed after the first key produced intervals of a semitone which can be represented by the letter S followed by an S. However the interval produced between the first and third key you pressed would have been a whole Tone which can be represented by the letter T. In other words think of a semitone as an S and a full tone or two semitones apart being a T
If you now go back to the original key you pressed, for arguments sake let us call it the key of C if you now go to two semitones the interval will be a T if you now go up another two semitones you will have another T, now go up just a semitone to produce an S then two semitones for another T then another T and another T and finally semitone or S you will have played a major scale named after the note you started on. The patter of which will have been TTS TTTS
So regardless of which key on the keyboard you first press, if you then go up following the intervals TTSTTTS you will play a major scale. Simple as that.