 [The opinion] which supposes these Essences, as a certain number of Forms or Molds, wherein all natural Things, that exist, are cast, and do equally partake, has, I imagine, very much perplexed the Knowledge of natural Things. The frequent Productions of Monsters, in all the Species of Animals, and of Changelings, and other strange Issues of humane Birth, carry with them difficulties, not possible to consist with this Hypothesis: Since it is as impossible, that two Things, partaking exactly of the same real Essence, should have different Properties, as that two Figures partaking in the same real Essence of a Circle, should have different Properties. (III.iii.17)