Why did the gentleman disapprove of having pictures of horses as wallpapers?

Gradgrind tells his students at his school that wallpaper with horses on it is unrealistic because horses do not in fact live on walls,

I interpret this as Dickens showing how extreme this philosophy can become—rejecting beauty and imagination in favor of cold logic. In my view, it highlights one of the novel’s central criticisms: that an education system based purely on facts risks stripping away essential human qualities like curiosity and emotional depth.

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