In the future, I will post articles about classical music's evolution over time. From Renaissance to Baroque to Classical on through Romantic and Modern and so forth. To best talk about these changes, you need to be able to understand what I mean when I say something like "sonata form". These concepts are not hard to follow however, they do require a basic understanding of music theory. For those of you who know some music theory, this will be review, and I hope you will forgive the time spent.
First off, a definition. Music Theory is, quite simply, the study of how music works. It studies how composers achieve their results; why a classical symphony sounds different from a baroque concerto. This is HEAVILY dependent (though not completely) upon the way music is written. There are many customs to writing music, but the most predominately used method has been the one passed down in Western music (i.e. European). This is the basic music staff and notes that you see everywhere. This is what allows people who play music to play the music that others have written in the way that these words and letters are a way for you to read the words that I have written, or recite a soliloquy from a play that was written by Shakespeare, and so on and so forth. It sounds basic, but it is absolutely essential, the bare bones and method of communication between people, in this case, musical communication, when not playing the instrument directly.
The difference between Treble and Bass clefs is the octave in which the notes sound. If you are not familiar, the first seven main notes in Western music you should learn are: C D E F G A B, after which comes another C and they continue higher (similarly going in the reverse direction for going downward). There are also an additional five notes that rest between these notes. These notes all have two names. A name reached by adding an Accidental, that would be a Sharp (#, which raises the pitch one half step) in front of one of the main notes, and a name reached by adding a Flat (b, which lowers the pitch one half step) in front of one of the main notes. These notes are C#/Db D#/Eb F#/Gb G#/Ab A#/Bb. The observant person will note that there is no E#/Fb or B#/Cb. This is because these two notes are naturally one half step apart and thus modifying by a half step achieves the next fully named note, negating the need for the accidental. These are the complete notes for every scale in Western music (for almost 1500 years). Modern music can make use of notes between these twelve, but for simplicity's sake, assume that every note that you hear or see written is one of these twelve unless it is specifically mentioned otherwise and you would be right a good 99.9999% of the time (an estimated statistic, though it emphasizes the point). There is also a symbol for a Natural (♮) which is simply a way of correcting the thought back to the regular note from the accidental, i.e. a B♮ is the same as a B, but might be used in conversation after talking about a bunch of notes that are Bb.
I have started with the letter C here instead of A (the natural beginning of the alphabet) because the C Major Scale is the single most basic building block of music. A Scale is a series of notes which is essentially the basis for a piece of music. This would be like saying that I have a pile of oak wood and all those blocks of oak wood is what I am going to be using to build my bookshelf. I will use things like nails, and maybe some glue to get the job done, which would be other notes defined by accidentals, but in the end, the majority of my new bookshelf will be comprised of that oak wood. There are many variations of scales, the most common being the Major Scale and the Minor Scale. The C Major Scale is thus: C D E F G A B C (it is generally the tradition when writing scales to reiterate the Tonic, i.e. the bottom/top note, though you can see it with the top C left off, in which case, you would always assume that the bottom note is the tonic and the note directly after the last note in the scale would be the tonic again).
On the music staff, each non-modified note, C D E ... B C, takes its place as is, with no accidentals. Notes that are sharp or flat share the same line or space with another note, e.g. a B Flat appears on the same line as the B, thus the need for the flat symbol illustrating that a different note is to be played. Given this, there are clearly multiples of each notes as well, two notes that are C that do not sound exactly the same. These notes are separated by an Octave, that would be, they sound almost exactly the same except that one is higher in pitch than the other, but when you play them together, they still sound very good together and become almost indistinguishable from each other when done well. The basis for keeping track of all these different notes then is determined by where on the staff they are. The note C higher on the staff than another C will obviously sound higher and vice versa. In the image above, as I mentioned, there are two staves (plural of staff), one with a Treble Clef and one with a Bass Clef.
As the words imply (in Italian), the Treble Clef is higher while the Bass Clef is lower. The middle line in the Treble Clef is a B, while the middle line in the Bass Clef is a D. Each successive line and space above and below those then are the next notes in either direction. Thus the Treble Clef lines, from bottom to top are E G B D F, while the spaces are F A C E, and the Bass Clef lines from bottom to top are G B D F A, while its spaces are A C E G. The two are related exactly by the note directly in the middle of them, the Middle C or C4 (not the explosive). It is called this because, on the piano, it is the middle of the 7 Cs, or the 4th one from the bottom, with C1 then being the first note on the left hand side and C7 being the last one on the right hand side. This Middle C (most refer to it that way, though I prefer C4) is located one the very next ledger line below the bottom of the Treble Clef staff and on the very next ledger line above the Bass Clef staff. The observant person will note then that the very first note on top of the Bass Clef in the first measure of that example above is the D located in the space directly below the Treble Clef, thus being the exact same note as the D located there in the beginning of the 3rd measure, this time on the upper staff (a Measure simply delineates one section of written music from another for ease of reading, and is indicated by a solid line stretching from the bottom line of the staff to the top line of the staff, in this case, since the grand staff is used, it stretches from the bottom of the bottom staff to the top of the top staff, thus clearly indicating a total of four measures, separated by three different measure lines).
The quality of the Scale is determined by the relationship between each note in the scale. Remember there are a total of twelve notes in western music, in order from C, bottom to top: C C#/Db D D#/Eb E F F#/Gb G G#/Ab A A#/Bb B C, each of which is then the very next direct note, there are no regular notes that can be found between these (this is called the Chromatic Scale). Given that then, the distance between any two of those successive notes in the chromatic scale is called a Half Step (e.g. C to Db or F to F#) while the distance between two notes in the situation of *note, skip one, note* from the chromatic scale is a Whole Step (e.g. G to A, skipping G#, or Bb to C, skipping B). The two main scales that are regularly used as the basis for most music are the Major and Minor Scales. These are called by their tonic note, i.e. the C Major Scale begins on a C. This is also then called the Key, as in the piece is in the key of C, or C Major (when not stated, the assumption is major, minor or otherwise will always be stated). From that note then, the Major Scale is constructed by then going up the following distances: whole step (C - D), whole step (D - E), half step (E - F), whole step (F - G), whole step (G - A), whole step (A - B), half step (B - C), thus completing the scale. The Minor Scale is constructed similarly, only starting on the 6th note of the major scale, e.g. the A Minor Scale: whole step (A - B), half step (B - C), whole step (C - D), whole step (D - E), half step (E - F), whole step (F - G), whole step (G - A). The observant person notices that in the major scale, the last note before the tonic again is separated by a half step, while in the minor scale it is a whole step. This quirk of scales and other scales not listed here are a topics for further articles, as well as anything else you see on the example above not mentioned in this post such as those big curvy lines or the 'f' that appears in the middle of the two staves.
This is a lot of information for someone who has never seen it before or is not familiar with it. To try and familiarize yourself with it if you do not play an instrument, my best recommendation would be to listen to music while watching the sheet music to the same piece. Easy examples to start with would be some Mozart piano sonatas, as you can find a lot of them on youtube edited so that the sheet music on the image corresponds exactly to the music being played, as in this example: Mozart, Piano Sonata No. 16 in C Major
