learn what a thought is.

In any such sentence as this, _Spiders spin_, something is said, or
asserted, about something. Here it is said, or asserted, of the animals,
spiders, that they spin.

The sentence, then, consists of two parts,--the name of that of which
something is said, and that which is said of it.

The first of these parts we call the +Subject+ of the sentence; the second,
the +Predicate+.

Now, if the sentence, composed of two parts, expresses the thought, there
must be in the thought two parts to be expressed. And there are two: viz.,
something of which we think, and that which we think of it. In the thought
expressed by _Spiders spin_, the animals, spiders, are the something of
which we think, and their spinning is what we think of them. In the
sentence expressing this thought, the word _spiders_ names that of which we
think, and the word _spin_ tells what we think of spiders.

Not every group of words is necessarily a sentence, because it may not be
the expression of a thought. _Spiders spinning_ is not a sentence. There is
nothing in this expression to show that we have formed a judgment, _i.e._,
that we have really made up our minds that spiders do spin. The spinning is
not asserted of the spiders.

_Soft feathers_, _The shining sun_ are not sentences, and for similar
reasons. _Feathers are soft_, _The sun shines_ are sentences. Here the
asserting word is supplied, and something is said of something else.