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Several people on this thread could use a refresher on the Fallacy of Composition and emergent properties:

Here’s another silly argument:

The atoms comprising this barrel of bricks are practically weightless.
So this barrel of bricks is practically weightless.

The predicate “practically weightless” is true of each atom; i.e., it is true of the barrel of bricks distributively, if you think of the barrel of bricks as a collection of atoms. Yet the predicate is clearly false when you think of the barrel of bricks as a whole; barrels of bricks have noticeable weight.
Arguments like this are said to commit the fallacy of composition. The fallacy of composition consists in assuming (wrongly) that predicate that applies to a subject distributively must also apply collectively.
These examples have been silly, but they point to deep philosophical issues. For example, many people would agree with the following argument:

Everything in the universe has a cause.
So the universe as a whole must have a cause.

Now, the predicate “caused” is true of everything in the universe (nothing is uncaused); in other words, the predicate “caused” is true of the universe distributively. But from that, can we be certain it’s true collectively as well? No, because we know that predicates true distributively are not necessarily true collectively. This argument commits the fallacy of composition.
Here’s another, more complex and extremely common argument:

All the individual cells comprising my body lack consciousness (i.e., no individual cell is conscious).
Therefore, my body can’t be conscious.
But I am conscious.
Therefore, I must be more than a mere body. I must have a mysterious non-physical component to account for my consciousness.

I hope you see that the move from (1) to (2) is clearly a fallacy of composition. What’s true of my cells (me distributively) is not necessarily true of me (me collectively). So the argument consisting of statements (2) through (4), though of modus tollens form and valid, is still unsound.
Emergent Properties
Some properties emerge only after you combine things into wholes. Such properties are called, not surprisingly, emergent properties. That’s often why what’s true of the parts isn’t necessarily true of the wholes, and vice-versa. Using John Searle’s famous example, being wet is an emergent property of water. None of the water molecules are wet. But wetness happens when you put enough of those molecules together. Obviously, then, the following argument is silly:

All the individual molecules comprising this water lack wetness.

Therefore, this water can’t be wet.
But this water is wet.
Therefore, this water must be more than these mere molecules. This water must have a mysterious non-physical component to account for its wetness.
The move from (1) to (2) is an obvious fallacy of composition because wetness is an emergent property. Searle says consciousness is an emergent property of brains just like wetness is an emergent property of water. Neither wetness nor consciousness necessarily requires anything non-physical to explain it.

Thanks for the refresher. However, some better examples are needed. In an attempt to learn something, let me stretch my neck for the ax. 1. The atoms comprising this barrel of bricks are practically weightless.

2. So this barrel of bricks is practically weightless.

Both atoms and the barrel (made of atoms) share the attribute of weight (or if not in a gravitational field, mass). The term 'practically weightless' is imprecise and subjective and misleading.

For example, many people would agree with the following argument:

1. Everything in the universe has a cause.

2. So the universe as a whole must have a cause.

Where do I start? This example is totally dependent on the definition of the attribute 'cause' and the assumption the first statement is true. And is the universe 'everything' or something apart and separate from 'everything'?

Here’s another, more complex and extremely common argument:

1.All the individual cells comprising my body lack consciousness (i.e., no individual cell is conscious).

2. Therefore, my body can’t be conscious.

This example depends on the definition of 'conscious'....which, IIRC, is a philosophical concept that by definition only applies to human beings The 'emergent property' (attribute) here is subjective. One could argue that individual atoms have no color but collectively they do. But this depends on the definition of color. If color is what the human eye detects, this is true. But if color is the wavelengths of light absorbed, reflected, or ignored, this is not true.