AC A 
parts added together make more than the 
whole number : thus the parts of 20, make 
22, viz. 1, 2, 4, 5, 10. 
ACACIA, in botany, a species of mimosa. 
See Mimosa. 
Acacia, in the materia medica of the 
ancients, a gum made from the Egyptian 
acacia-tree, and thought to be the same 
with our, gum-arabic. 
ACADEMICS, a sect of philosophers 
who followed the doctrine of Socrates and 
Plato, as to the uncertainty of knowledge, 
and the incomprehensibility of truth. 
Academic, in this sense, amounts to much 
the same with Platonist; the difference be- 
tween them being only in point of time. 
They who embraced the system of Piato, 
among the ancients, were called Academic!; 
whereas those who have done the same, 
since the restoration of learning, have as- 
sumed the denomination of Platonists. We 
usually reckon three sects of Academics ; 
though some make five. The ancient Aca- 
demy was that which was founded by Plato ; 
and consisted of those followers of this emi- 
nent philosopher; who taught the doctrine 
of their master without mixture or corrup- 
tion. The first of these was Speusippus; 
he was succeeded by Xenocrates. After 
his death the direction of the academy de- 
volved upon Polemo,and then upon Crates, 
and terminated with Crantor. After the 
death of Crates, a new tribe of philosophers 
arose, who, on account of certain innovations 
in their manner of philosophising, which in 
some measure receded from the Platonic 
system, without entirely deserting it, have 
been distinguished by the appellation of the 
Second, or Middle Academy. . The first 
preceptor who appears in this class, and 
who, in consequence cf the innovations 
which he introduced into the Platonic school, 
has been commonly considered as the foun- 
der of this' academy, is Arcesilaus. Before 
the time of Arcesilaus, it was never denied, 
that useful opinions may be deduced from 
the senses. Two sects arose about this 
time, which threatened the destruction of 
the Platonic system ; one was founded by 
Pyrrho, which held the doctrine of universal 
scepticism, and the other by Zeno, which 
maintained the certainty of human know- 
ledge, and taught with great confidence a 
doctrine essentially different from that of 
Plato. In this situation, Arcesilaus thought 
it necessary to exercise a cautious reserve 
with regard to the doctrine of his master, 
• and to conceal Ins opinions from the vulgar, 
ander the appearance of doubt and uncer- 
AC A 
tainty. Professing to derive his doctrine 
concerning the uncertainty of knowledge 
from Socrates, Plato, and other philoso- 
phers, he maintained, that though there is a 
real certainty in the nature of things, every 
thing is uncertain to the hitman understand- 
ing, and consequently that all confident as- 
sertions 'are unreasonable. He thought it 
disgraceful to assent to any proposition, the 
truth of which is not fully established, and 
maintained that, in all questions, opposite 
opinions may be supported by arguments ot 
equal weight. He disputed against the 
testimony of the senses, and the authority of 
reason; acknowledging at the same time, 
that they furnish probable opinions sufficient 
for the conduct of life. However, his secret 
design seeins to have been to establish the 
doctrine of Plato, that the knowledge de- 
rived from sensible objects is uncertain, and 
that the only true science is that which is 
employed upon the immutable objects of 
intelligence, or ideas. 
After the death of Arcesilaus, the Platonic 
school yvas successively under the care ot 
Lacydes, who is said to have founded a new 
school, merely because he changed the 
place of instruction, and held it in the gar- 
den of Attalus, within the limits of the Aca- 
demic grove, and of Evander and Egesinus. 
Arcesilaus, however, had opposed the Stoics 
and other dogmatical philosophers, with 
such violence, and extended his doctrine of 
uncertainty so far, as to alarm not only the 
general body of philosophers, who treated 
him as a common enemy to philosophy, but 
even the governors of the state, who appre- 
hended that his opinions would dissolve all 
the bonds of social virtue and of religion. 
His successors, therefore, found it difficult to 
. support the credit of the academy; and 
Carneades, one of the disciples of tins school, 
relinquished, at least in words, some of the 
more obnoxious tenets of Arcesilaiis, 
From this period the Platonic school as- 
sumed the appellation of the New Academy, 
which may be reckoned the third in order 
from its first establishment. It was the 
doctrine of this academy, that the senses, 
the understanding, and the imagination, fre- 
quently deceive us, and therefore cannot be 
infallible judges of truth; but that, from the 
impressions produced on the mind, by means 
of the senses, called by Carneades phantasies, 
or images, we infer appearances of truth, or 
probabilities. These images do not always 
correspond to the real nature of things, and 
there is no infallible method of determining 
when they are true or false ; and conse- 
