SEPTEMBER 28, 1916] 
NATURE 
81 
he solution I am asking for is not a phrase however 
rilliant, but a solid branch of science, constructed 
ith slow patience, showing in detail how the corre- 
ondence is effected. 
The first great steps in the organisation of thought 
ere due exclusively to the practical source of scientific 
activity, without any admixture of theoretical impulse. 
‘Their slow accomplishment was the cause and also 
the effect of the gradual evolution of moderately 
rational beings. I mean the formation of the concepts 
of definite material objects, of the determinate lapse 
of time, of simultaneity, of recurrence, of definite 
relative position, and of analogous fundamental ideas, 
according to which the flux of our experiences is men- 
tally arranged for handy reference : in fact, the whole 
apparatus of common-sense thought. Consider in your 
“mind some definite chair. The concept of that chair 
is simply the concept of all the interrelated experiences 
connected with that chair—namely, of the experiences 
of the folk who made it, of the follk who sold it, of 
the folk who have seen it or used it, of the man who 
is now experiencing a comfortable sense of support, 
_ combined with our expectations of an analogous future, 
_ terminated finally by a different set of experiences when 
the chair collapses and becomes fire-wood. The forma- 
tion of that type of concept was a tremendous job, and 
zoologists and geologists tell us that it took many tens 
of millions of years. I can well believe it. 
I now emphasise two points. In the first place, 
science is rooted in what I have just called the whole 
apparatus of common-sense thought. 
datum from which it starts, and to which it must 
recur. We may speculate, if it amuses us, of other 
beings in other planets who have arranged analogous 
experiences according to an entirely different conceptual 
code—namely, who have directed their chief attention 
to different relations between their various experiences. 
But the task is too complex, too gigantic, to be revised in 
its main outlines. You may polish.up common sense, 
you may contradict it in detail, you may surprise it. 
But ultimately your whole task is to satisfy it. 
In the second place, neither common sense nor 
science can proceed with its task of thought organisa- 
tion without departing in some respect from the strict 
consideration of what is actual in-experience. Think 
again of the chair. Among the experiences upon which 
its concept is based I included our expectations of 
its future history. I should have gone further and 
included our imagination of all the possible experiences 
which in ordinary language we should call percep- 
tions of the chair which might have occurred. This 
is a difficult question, and I do not see my way through 
it. But at present in the construction of a theory of 
space and of time there seem insuperable difficulties 
if we refuse to admit ideal experiences. 
This imaginative perception of experiences, which, 
if they occurred,. would be coherent with our actual 
experiences, seems fundamental in our lives. It is 
neither wholly arbitrary nor yet fully determined. It 
is a vague background which is only made in part 
definite by isolated activities of thought. Consider, for 
example, our thoughts of the unseen flora of Brazil. 
Ideal experiences are closely connected with our 
imaginative reproduction of the actual experiences of 
other peovle, and also with our almost inevitable con- 
ception of ourselves as receiving our impressions from 
an external complex reality bevond ourselves. It may 
be that an adequate analysis of every source and every 
type of experience yields demonstrative proof of such 
a realitv and of its nature. Indeed, it is scarcely to be 
doubted that this is the case. The precise elucidation 
of this question is the problem of metaphysics. One 
of the points which I am urging in this address is 
that the basis of ‘science does not depend on the 
assumption of any of the conclusions of metaphysics; 
NO. 2448, Vor. 98] 
That is the 
but that both science and metaphysics start from the 
same given groundwork of immediate experience, and 
in the main proceed in opposite directions on their 
diverse tasks. 
For example, metaphysics inquires how our percep- 
tions of the chair relate us to some. true reality. 
Science gathers up these perceptions into a determinate 
class, aads to them ideal perceptions of an analogous 
sort, which in assignable circumstances would be ob- 
tained, and this single concept of that set of percep- 
tions is all that science needs; unless indeed you prefer 
that thought find its origin in some legend of those 
great twin brethren, the Cock and Bull. 
My immediate problem is to inquire into the nature 
of the texture of science. Science is essentially logical. 
The nexus between its concepts is a logical nexus, 
and the grounds for its detailed assertions are logical 
grounds. King James said, ‘‘No bishops, no king.”’ 
With greater confidence we can say, ‘*No logic, no 
science.’’ The reason for the instinctive dislike which 
most men of science feel towards the recognition of 
this truth is, I think, the barren failure of logical 
theory during the past three or four centuries. We 
may trace this failure back to the worship of authority 
which in some respects increased in the learned world 
at the time of the Renaissance. Mankind then changed 
its authority, and this fact temporally acted as an 
emancipation. But the main fact, and we can find 
complaints' of it at the very commencement of the 
modern movement, was the establishment of a rever- 
ential attitude’ towards any statement made by a 
classical author. Scholars became commentators on 
truths too fragile to bear translation. A science which 
hesitates to forget its founders is lost. To this hesi- 
tation I ascribe the barrenness of logic. 
It will be necessary to sketch in broad outline some 
relevant features of modern logic. . . . 
I will now break off the exposition of the function 
of logic in connection with the science of natural 
phenomena. I have endeavoured to exhibit it as the 
organising principle, analysing the derivation of the 
concepts from the immediate phenomena, examining 
the structure of the general propositions which are the 
assumed laws of nature, establishing their relations to 
each other in respect to reciprocal implications, deduc- 
ing the phenomena we may expect in given circum- 
stances. 
Logic, properly used, does not shackle thought. It 
gives freedom and, above all, boldness. Illogical 
thought hesitates to draw conclusions, because it never 
knows either what it means, or what it assumes, or 
how far it trusts its own assumptions, or what will 
be the effect of any modification of assumptions. Also 
the mind untrained in that part of constructive logic 
which is relevant to the subject in hand will be ignorant 
of the sort of conclusions which follow from various 
sorts of assumptions, and will be correspondingly dull 
in divining the inductive laws. The fundamental 
training in this relevant logic is, undoubtedly, to 
ponder with an active mind over the known facts of 
the case, directly observed. But where elaborate de- 
ductions are possible, this mental activity requires for 
its full exercise the direct studv of the abstract logical 
relations. . This is applied mathematics. 
Neither logic without observation, nor observation 
without logic, can move one step in the formation of 
science. We may conceive humanity as engaged in an 
internecine conflict between youth and age. Youth is 
not defined by years, but by the creative impulse to 
make something. The aged are those who, before all 
things, desire-not to make a mistake.. Logic is the 
olive branch from the old to the young, the wand 
which in the hands of youth has the magic property 
of creating science. 
1 £.g. in 155“ by Ita ian sckoolmen. 
