thoughts and practice a little further, and then it will plainly appear.  The well-shaped changeling is a man, has a rational soul, though it appear not:  this is past doubt, say you:  make the ears a little longer, and more pointed, and the nose a little flatter than ordinary, and then you begin to boggle:  make the face yet narrower, flatter, and longer, and then you are at a stand:  add still more and more of the likeness of a brute to it, and let the head be perfectly that of some other animal, then presently it is a monster; and it is demonstration with you that it hath no rational soul, and must be destroyed.  Where now (I ask) shall be the just measure; which the utmost bounds of that shape, that carries with it a rational soul?  For, since there have been human foetuses produced, half beast and half man; and others three parts one, and one part the other; and so it is possible they may be in all the variety of approaches to the one or the other shape, and may have several degrees of mixture of the likeness of a man, or a brute;—­I would gladly know what are those precise lineaments, which, according to this hypothesis, are or are not capable of a rational soul to be joined to them.  What sort of outside is the certain sign that there is or is not such an inhabitant within?  For till that be done, we talk at random of man:  and shall always, I fear, do so, as long as we give ourselves up to certain sounds, and the imaginations of settled and fixed species in nature, we know not what.  But, after all, I desire it may be considered, that those who think they have answered the difficulty, by telling us, that a mis-shaped foetus is a monster, run into the same fault they are arguing against; by constituting a species between man and beast.  For what else, I pray, is their monster in the case, (if the word monster signifies anything at all,) but something neither man nor beast, but partaking somewhat of either?  And just so is the changeling before mentioned.  So necessary is it to quit the common notion of species and essences, if we will truly look into the nature of things, and examine them by what our faculties can discover in them as they exist, and not by groundless fancies that have been taken up about them.

17.  Words and Species.

I have mentioned this here, because I think we cannot be too cautious that words and species, in the ordinary notions which we have been used to of them, impose not on us.  For I am apt to think therein lies one great obstacle to our clear and distinct knowledge, especially in reference to substances:  and from thence has rose a great part of the difficulties about truth and certainty.  Would we accustom ourselves to separate our contemplations and reasonings from words, we might in a great measure remedy this inconvenience within our own thoughts:  but yet it would still disturb us in our discourse with others, as long as we retained the opinion, that species and their essences were anything else but our abstract ideas (such as they are) with names annexed to them, to be the signs of them.