A simple shape grammar generating Celtic knots is presented producing spirals, step patterns and key patterns in the style. The second vignette in the series shows the design of a Celtic knot pattern using four rules that capture the growth of the pattern from a single loop to an alternating loop. Two of these rules capture the growth along its main horizontal and vertical axes and two of them resolve its corner conditions. The shape rules apply to shapes composed of arcs and straight lines under isometry transformations.