Owen—-Interrogative Thought—Means of Its Expression. 427 
say the interlocking pair of judgments, which I have sought to 
diagram, by 
I wish you to tell me void-filler 
killed 
Lincoln 
At first sight all our effort, yours as well as mine, may seem 
to be hardly worth the while. The common, factor of the judg¬ 
ments is, in a first condition of my mind, a mental zero, and 
later merely an unknown quantity, blow zero once is zero 
again; and an unknown quantity is not made known by repeti¬ 
tion. Yet everyone remembers that the value of an algebraic 
x, though unrevealed by either of two equations, may some times 
be obtained from their cooperation. Indeed, the case presented by 
my diagram is to a certain extent analogous. I use an unknown 
quantity in each one of two judgments. In one of these 1 1 expect 
you to obtain for the unknown term a substitute in terms of the 
known—and, having done so, to 1 use it in the other judgment. 
But, dropping algebraic illustration, I wish to center attention 
on the case in hand. 
I concede that my pair of judgments would disappoint my 
purpose, were your knowledge no greater than my own. But 
what is unknown to me is supposed to be known to you. On 
my side the desired idea forms no part of mental stock. But on 
your side it is a part of mental stock. Your only difficulty is to 
find it—to select it from its fellows. If then, while letting you 
know that I wish you to tell me an idea, I successfully direct 
you to its selection among the ideas in your possession, you will 
be enabled to fulfill my wish. What needs to be established, 
then, is your susceptibility to such direction. 
In the effort to exhibit this, I substitute for ‘Void-filler” the 
convenient x, and diagram the chosen illustration of the inter¬ 
rogative judgment now considered, by 
I desire you to tell me x 
killed 
Lincoln 
On reading this, I assume that you admit to mind what I will 
call a horizontal thought (because expressed by words in hori¬ 
zontal series), and also a perpendicular thought. Under the in- 
