You may of noticed that immediately after the clef and key signature the 'time signature' is shown by 2 numbers - one on top of the other. For the moment it is only necessary to regard the upper figure as showing the amount of beats in each bar, and the lower figure indicating the type of note that gets the beat. Therefore if the top number is 4 then their are 4 beats in every bar. If the bottom number is 4 then the beats are the value of a crotchet. So now you know that 4=crotchet. This is because a crotchet (quarter-note) is one ¼ of a semi-breve (whole-note) Now you know why our clever colonial cousins in the US re-named the notes.
 
The table below illustrates the hierarchical 'pyramid' of notes and which are represented by the lower figure in the time signature. You can clearly see how the number represents the amount of notes that make up a semi-breve (whole-note).

	Semibreve  (Whole-note)	1	In the time signature this would be the bottom figure (rare or never)
	Minims (Half-notes)	2	Commonly used
	Crotchets (Quarter-notes)	4	Commonly used
	Quavers (Eighth-notes)	8	Commonly used but only ⅜ in Grade 1 (see Ex.9)
	Semi-Quavers (Sixteenth- notes)	16	Will be covered later