In a Sharp Key signatures, does a Si Sharp equal a Do on the piano itself?

[irontheater]

I'm still fairly new to this all, and teaching myself step by step, but I couldn't help but notice how weird that was.

Also, if a note doesn't have a Sharp, (let's say Mi), does that mean that in a Sharp Key Signature it should be played as a Fa, or as a Mi?

[nystul]

Making a note sharp always raises it one semitone from its natural position, even if that corresponds to another white key on the piano.  So yes, on keyboard instruments, B# is the same physical key as C, and E# is the same physical key as F.  The reverse is also true.  Cb is the same piano key as B and Fb is the same piano key as E.

It is somewhat rare to see any of these notes in the key signature.  As things work out, they are the last 2 sharps or flats that can be added.  So you will need at least 6 sharps or flats in the key signature in order to have one of these examples.  Of course, they also are added as accidentals (sharp or flat added directly to the note) in some situations.

[nyiregyhazi]

I'm still fairly new to this all, and teaching myself step by step, but I couldn't help but notice how weird that was.

Also, if a note doesn't have a Sharp, (let's say Mi), does that mean that in a Sharp Key Signature it should be played as a Fa, or as a Mi?

In a sense, yes. But just visualise any sharp as being raised from its reference note. Never forget where it came from.

[iansinclair]

and no, there are many times when it doesn't seem to make a bit of sense!  I mean, why write a B#, when you could write a C?  Usually what it is, though, is to help make better sense of an harmonic progression of some kind.  For some really good examples, analyze the harmonic sequences in the Chopin Op. 27 No. 1 Nocturne, which is in C# minor, but ends in C# major (which has an E# in the chord) -- and has a short section in the middle in Dflat, just to make it more interesting!

[nyiregyhazi]

and no, there are many times when it doesn't seem to make a bit of sense!  I mean, why write a B#, when you could write a C?

Are you unfamiliar with the concept of a raised 7th? It would be plain stupid to notate a C natural then c sharp if avoidable, regardless of harmony. B sharp is almost always closely followed by a C sharp. These things are very simple to conceive when you simply pair it off against the tonic, a semitone away. It's very rare that these notes are not very clearly paired with a neighbour note, and likewise with double sharps. I've very rarely encountered a single instance of this where it wasn't clearly sensible to want to avoid repeating the same note with endless symbols. Harmony can play a role but it's as important in single lines.

[j_menz]

and no, there are many times when it doesn't seem to make a bit of sense!  I mean, why write a B#, when you could write a C? 

I actually find it easier to read if it's a B#.  The sequence of sharps (or flats) means that B# means I expect lots of other sharps, but C natural means I have to force myself to consciously remember they're there.

[iansinclair]

Are you unfamiliar with the concept of a raised 7th? It would be plain stupid to notate a C natural then c sharp if avoidable, regardless of harmony. B sharp is almost always closely followed by a C sharp. These things are very simple to conceive when you simply pair it off against the tonic, a semitone away. It's very rare that these notes are not very clearly paired with a neighbour note, and likewise with double sharps. I've very rarely encountered a single instance of this where it wasn't clearly sensible to want to avoid repeating the same note with endless symbols. Harmony can play a role but it's as important in single lines.

After some 50 years as a professional musician and conductor (FAGO, FRCO for diploma status), I would hope that I was at least mildly familiar with the notion of a raised 7th.  However, I do not think that it would be fair of me -- or anyone else helping a student -- to assume that the student, in this case, the OP, would be, and to them it might easily appear that the use of, in this case, C natural instead of B# where either the harmonic or melodic sequence requires it -- but where they, without the benefit perhaps of your extensive knowledge of music and music theory -- was a bit odd.

[nyiregyhazi]

After some 50 years as a professional musician and conductor (FAGO, FRCO for diploma status), I would hope that I was at least mildly familiar with the notion of a raised 7th.  However, I do not think that it would be fair of me -- or anyone else helping a student -- to assume that the student, in this case, the OP, would be, and to them it might easily appear that the use of, in this case, C natural instead of B# where either the harmonic or melodic sequence requires it -- but where they, without the benefit perhaps of your extensive knowledge of music and music theory -- was a bit odd.

Ah, fair enough. To a layman though, I think the simplest method is to appreciate neighbouring notes. I never think of a b sharp as being like a c, as 90 percent of the time there's a c sharp next to it or soon to follow. Even if not, when you imagine a sense of mental connection to an imaginary c sharp, it feels simple. It would be most ungainly to keep adjusting one letter back and forth. Even to mentally think of it as really being a c is actually more confusing. Although harmony and scale knowledge helps, these kinds of mental attachments can be made without it.