If asked whether I like Piet Mondrian’s paintings, I’d say, cautiously, that I do. The caution reflects a sense of unworthiness; the syncopated grids, randomly occupied by blocks of red, blue and yellow, cheer me up.

The optical illusion whereby the intersections of the black lines turn into elusive white dots when you aren’t directly looking at them is-dare I use the word?-jolly. Visiting the Courtauld’s ‘Mondrian || Nicholson: in Parallel’, I find he wasn’t jolly at all, but intensely serious, agonising for months over the placing of a single line.

It’s a fine show, focused on the years 1938-40 when Mondrian worked next door to Nicholson in Hampstead. Had Nicholson, like Mondrian, gone to New York rather than St Ives, think how much more valuable he’d be in the sale rooms. But Mondrian’s style did suit a city laid out like a waffle. Which artist do you prefer?

The debate was fierce over Mondrian muffins in the tea room. But best of all was the impetus we’d been given to revisit the rest of the gallery. After the crowds that had packed Tate Modern’s Gauguin exhibition, the absence of spectators in the Courtauld could have induced kenophobia (or, in plain English, a terror of empty rooms). There was no one in the Cézanne part. But sssh, I don’t want the secret to get out.