H
- Happiness: [24], [30]
- Homogeneous, Instability of: [98]
- Human nature (see Uniformity)
- Huxley, Professor: [24], [28], [30], [33], [39], [120], [144], [149]-[59], [173], [204], [205], [208], [213], [219], [247], [286]-[8]
I
- Idealism: [38]-[59]
- Ideals: [30]-[2], [34], [41], [54], [74], [164]-[84], [194], [195], [204]-[36], [241]-[73], [280] (see Moral ideal, Truth)
- Identity: [201]
- Illusion: [17], [22], [23]-[5], [44], [45], [47], [57], [60], [65], [74], [112], [136], [164], [165], [227], [243], [246], [247], [256], [260]
- Independence: [201]
- Inhumanity: [33]
- Instinct: [236]
- Interaction: [68]
K
L
M