Biology Reference
In-Depth Information
probabilistic process. This is necessary because, while calculation of
probabilities pervades all scientific fields, the nature of the process
is still very poorly understood. There are frequently confusions
related to using it, including in scientific papers. They come from
modes of essentialist thought which are contrary to modern scien-
tific practice. They consist in confusing notions of accident, contin-
gency and noise with the notion of probability.
2.1
There is no qualitative difference between determinism
and probabilism
We all have some idea of what differentiates a deterministic system
from a probabilistic system. We think we know with certainty that
certain phenomena are invariably repeated when the same cause is
activated. For example, if I let go of this pen I am holding in my
hand I have absolutely no doubt that it will fall, and that that is
what will happen every time I let it go in the future. This is an
event subject to determinism and I can say that the system gov-
erned by gravity, including myself holding the pen, and the ground,
is a deterministic system. We also know that the type of situation
that I have just described is not universal. There are other phe-
nomena for which there is no sole certain effect but which may have
several effects resulting from the same cause. The standard exam-
ple of this is the game of heads or tails. When I toss the coin there
are two possible results and I cannot say with certainty whether the
result will be heads or tails. This system is probabilistic. In addi-
tion, I do not need to be a great mathematician to know that each
of these two events has only a 50% chance (1 in 2 probability) of
occurring. I also know that probability is always between 0 and 1
and that the frequency of an event occurring when it is repeated
several times is all the greater the closer its probability is to 1.
When the probability is equal to 1, the event is always reproduced.
The difference between a deterministic system and a probabilistic
system is therefore connected with the value of probability. This
can be expressed quite simply: a deterministic system is a system
in which the probability of events occurring there is equal to 1,
