In the previous lessons we have discussed some pawn endgames and have introduced chess concepts like the King on the sixt rank and key squares. Another very useful concept is the opposition.
We can distinguish the vertical and the horizontal opposition.
The vertical opposition occurs when two kings face each other on a file with only one square in between. This is the normal opposition and we have seen something from this opposition in the lesson about the King on the sixth rank.
The horizonal opposition occurs when two kings are on the same rank with only one square in between. This is something we have seen before in the lesson about the rook pawn.

In addition to this vertical and horizontal oppsition we also have a diagonal opposition, a distant opposition and a virtual opposition. Concepts like key squares and opposition are strongly related. Having the opposition enables you to occupy a key square.

		Distant opposition In the distant opposition both kings are on the same file, rank or diagonal, but there is an odd number of squares (3 or 5) in between. The diagram on the left gives an overview of the vertical distant opposition. Kings in distant opposition will often maneuver to a more simple position of direct opposition.
		Virtual opposition In the virtual opposition both Kings are on the same coloured square which are two of the corners of a rectangle with corners of the same colour. The diagram on the left gives an example. The two corners of the rectangle that are not occupied by the kings are indicated by an x. White has the (virtual) opposition. The virtual opposition is in fact the most generic concept. If the rectangle becomes a square it is called the diagonal opposition. If the rectangle transforms into a line we have the vertical or horizontal distant opposition and if there is only one square between the two kings we have the normal opposition.

In the next lesson we will use the knowledge of the different forms of opposition in a discussion about the endgame in one of the Staunton-Williams games (London 1851).