Learning systems

Where English compares apples and oranges, German compares apples with pears: Äpfel mit Birnen vergleichen. The fruit differs and the verdict is the same — two things are being set side by side that cannot fairly be measured against each other. In this field the phrase earns its keep. Two scores taken on different test data, a model tuned on data the other never saw, last year’s figure set beside this year’s on a changed benchmark: each is ein Vergleich von Äpfeln mit Birnen, and a German reviewer will say so in those words. The idiom also packs into a compound, ein Äpfel-mit-Birnen-Vergleich, hyphenated all the way through, and it turns up with a different verb when unlike things are totted up into one figure: Äpfel und Birnen zusammenzählen. That is what an average taken across unrelated tasks does, and it is the most common way a single headline number hides what it is made of.