Terumot, Chapter One Mishnah One
The first mishnah in Terumot deals with who may separate terumah from a persons produce such that the separation is considered valid. We shall see that there are several important principles that make one qualified to separate terumah.
Five may not give terumah, and if they do so, their terumah is not considered terumah:
1) A heresh (deaf-mute); an imbecile, a minor,
2) And the one who gives terumah from that which is not his own.
3) If a non-Jew gave terumah from that which belongs to an Israelite, even if it was with his permission, his terumah is not terumah.
Section one: According to the rabbis, the deaf-mute, the imbecile (who is either mentally retarded or crazy) and the minor all lack legal liability for their actions. In Hebrew they say that they do not have daat which I usually translate as awareness of the consequences of their actions. I should stress that in the ancient world, sign language as we know it did not exist and this made it basically impossible to educate and even communicate with a deaf-mute. Sign language and the incorporation of the deaf into society is a relatively recent development.
Since these people lack legal awareness of the consequences of their action, they cannot declare something to be terumah, even if it belongs to them.
Section two: The produce must belong to the person who separates the terumah from it.
Section three: A non-Jew cannot separate terumah, even if the Israelite gave him permission to do so. This implies that if a Jew gave permission to another Jew to separate terumah, he can do so. A non-Jew cannot because he himself is not obligated in the laws of terumah.