The One-Ahead Principle

This is one of the oldest, and, at the same time, one of the
simplest methods ever devised for secretly reading questions. It
has been used by mind readers, pseudospiritualists and others
with great success for many years before both large and small
audiences. As originally performed, it was not a one-man effect;
hence, we shall first describe it that way and then give the
variations used by the single performer.

Original One-Ahead Method
The spectators are requested to write their questions on slips of
paper and to let no one see what they have written. These slips
are then folded by the writers so the writing is concealed on the
inside. Envelopes may be furnished and the questions sealed
within, if desired. This is a fair sized audience where some write
questions and some do not.
In any event, a total stranger is directed to collect the questions
and dump them on the table on the platform. The performer
picks up one of the sealed envelopes, holds it to his forehead, as
though to "see" with supernatural vision and shortly announces
that he "gets" the initials M. C.--"is M. C. present?" M.C.
acknowledges that she wrote a question, whereupon the
performer proceeds to give a suitable answer to her question
about a trip to Boston, etc. As he finishes the answer, the
performer tears open the envelope and reads aloud the question,
"Will I go to Boston? M. Clark."
That is what he appears to do, but all is not what it seems. M.
Clark wrote a question all right, but M. Clark is a confederate of
the performer's, and wrote that question by agreement, secretly
bending over a corner of her envelope so as to distinguish it
from the others, identifying it as the one to be avoided until the
last. The performer has picked up and opened some other
envelope, first pretending that it belongs to M. C. Then, as he
looks at the open slip, he orally reads "Will I go to Boston? M.
C.", but, in reality, he is at the same time mentally reading and
remembering the question written on the genuine slip before
him--let us assume this slip hears the question, "Will father get
well?--signed John Jones."
The performer has thus apparently confirmed his divination of
the first question, and now knows a genuine question which he
pretends to be the one contained in the next (second) envelope,
which he reads while held at the forehead as before. The same
procedure is followed throughout, each new envelope torn open
furnishing the data for the next reading.
The performer can stop at any time but if he desires to read all
of the questions, he leaves the M. Clark envelope till last, and
after it is torn open to apparently confirm the last test, it is
tossed among the others, and they may all be returned to the
writers.