" ... these two terms—the human spirit and the rational soul—designate one and the same thing."

"The vegetable spirit is that power of growth which is brought about in the seed through the influence of other created things.

The animal spirit is that all-embracing sensory power which is realized through the composition and combination of the elements. When this composition disintegrates, that spirit likewise perishes and becomes non-existent. It may be likened to this lamp: When oil, wick, and flame are brought together and combined, it is lit; and when this combination disintegrates—that is, when the constituent parts are separated from one another—the lamp also is extinguished.

The human spirit, which distinguishes man from the animal, is the rational soul, and these two terms—the human spirit and the rational soul—designate one and the same thing. This spirit, which in the terminology of the philosophers is called the rational soul, encompasses all things and as far as human capacity permits, discovers their realities and becomes aware of the properties and effects, the characteristics and conditions of earthly things. But the human spirit, unless it be assisted by the spirit of faith, cannot become acquainted with the divine mysteries and the heavenly realities. It is like a mirror which, although clear, bright, and polished, is still in need of light. Not until a sunbeam falls upon it can it discover the divine mysteries."

‘Abdu’l-Bahá, Some Answered Questions