1
Core logical function
Introduce an explanation, correction, or more exact restatement of what precedes.
Example
The species is nocturnal; that is, it is active mainly at night.
that is
/ðæt ɪz/ · that IZclarification transition
Introduce an explanation, correction, or more exact restatement of what precedes.
Use that is to express this relationship precisely: introduce an explanation, correction, or more exact restatement of what precedes.
What that is Really Means
The word becomes easier to use when its closely related senses are separated and compared.
2
Sentence connection
Use this expression in its normal grammatical frame so the relationship between the surrounding ideas remains explicit.
Example
The effect was localised—that is, it appeared only in the eastern plots.
3
Argument-level effect
It tells the reader how to interpret the timing, scope, evidence, contrast, condition, or consequence in the statement.
Example
Only one variable changed, that is, the temperature of the solution.
Use that is Naturally
Notice how the surrounding noun or clause reveals the exact shade of meaning.
The species is nocturnal; that is, it is active mainly at night.
The effect was localised—that is, it appeared only in the eastern plots.
Only one variable changed, that is, the temperature of the solution.
Precision Matters
That is overlaps with several common words, but each carries a different emphasis.
that is
vs.Means introduce an explanation, correction, or more exact restatement of what precedes.
in other words
Means restate an idea in clearer, simpler, or more explicit terms.
that is
vs.Means introduce an explanation, correction, or more exact restatement of what precedes.
put differently
Means restate an idea in another way to clarify its meaning or implication.
that is
vs.Means introduce an explanation, correction, or more exact restatement of what precedes.
namely
Means identify exactly what a preceding general reference means or includes.
that is
vs.Means introduce an explanation, correction, or more exact restatement of what precedes.
in effect
Means state what something amounts to in practice or restate its essential implication.
Test that is in Context
The second clause explains the meaning of the description in the first.
1
The treaty was bilateral; ___, it created obligations for exactly two states.