We Assign a Change in Identity Based on Our Perception of the Change Relative to the Whole

A mass of matter, with contiguous and connected parts, is placed before us.

We attribute a perfect identity to this mass, provided all the parts are unchanged.

But if some very small part were added to or subtracted from the mass, it would absolutely destroy the whole’s identity, strictly speaking.

• Yet we seldom think so accurately.
• We say the mass is the same despite this trivial change.

The thought passes so smoothly and easily from the object before the change to the object after it.

• We do not perceive the transition.

We imagine that it is just a continued survey of the same object.

A very remarkable circumstance attends this experiment.

The change of any considerable part in a mass of matter destroys the whole identity.

• But we must measure the greatness of the part by its proportion to the whole, and not absolutely.

The addition or reduction of a mountain would not be enough to produce a diversity in a planet.

• But the change of a very few inches can destroy the identity of some bodies.

This means that objects break the continuity of the mind’s actions according to their proportion to each other, and not according to the size of the objects.

• This interruption makes an object cease to appear the same.

The uninterrupted progress of the thought which constitutes the imperfect identity. This may be confirmed by another phenomenon.

A change in any considerable part of a body destroys its identity.

But it is remarkable that where the change is produced gradually and insensibly, we are less apt to ascribe to it the same effect.

The only reason is that when the mind follows the successive changes of the body: it feels an easy passage from surveying its condition in one moment to the view it in another, and it perceives no interruption in its actions.

From this continued perception, it ascribes a continued existence and identity to the object. We might use precautions in: introducing the changes gradually, and making them proportional to the whole. We make a scruple of ascribing identity to such different objects, when the changes finally become considerable.

We may induce the imagination to advance a step further by producing a: reference of the parts to each other, and combination to some common end or purpose.

A ship, with a big part changed by frequent repairs, is still the same ship.

The difference of the materials does not hinder us from ascribing an identity to it.

The common end, in which the parts conspire:

• is the same under all their variations, and
• affords an easy transition of the imagination from one bodily situation to another.

But this is still more remarkable when we:

• add a sympathy of parts to their common end, and
• suppose that they bear to each other the reciprocal relation of cause and effect in all their operations.

This is the case with all plants and animals.

Their several parts have a:

• reference to some general purpose, and
• mutual dependence on, and connection with each other.

After a few years, both plants and animals undergo a total change.

Yet we still ascribe identity to them, while their form, size, and substance are entirely altered.

This is the effect of so strong a relation.

An oak that grows from a small plant to a large tree is still the same oak.

• Though none of its parts are the same.

A baby becomes a man.

• He is sometimes fat or lean without any change in his identity.