"At times my heart delights in thinking of you and your future. And yet at times I cannot rid myself of ideas which arouse in me sad forebodings and fear when I am struck as if by lightning by the thought: is your heart in accord with your head, your talents? Has it room for the earthly but gentler sentiments which in this vale of sorrow are so essentially consoling for a man of feeling? And since that heart is obviously animated and governed by a demon not granted to all men, is that demon heavenly or Faustian? Will you ever -- and that is not the least painful doubt of my heart -- will you ever be capable of truly human, domestic happiness? Will -- and this doubt has no less tortured me recently since I have come to love a certain person [Marx's then-fiancee, Jenny von Westfalen] like my own child -- will you ever be capable of imparting happiness to those immediately around you?"