Except after an introductory dependent clause, do not use a comma to separate a dependent clause from a main clause unless the dependent clause provides nonessential information. See also Restrictive and Nonrestrictive Modifiers.
Ever since the atomistic view of matter came to be accepted, it has been
a burning question, how to see into the microworld of
molecular chemistry.
Ever since the atomistic view of matter came to be accepted, it has been
a burning question how to see into the microworld of molecular chemistry.
--Adapted from Philip Ball, Designing the Molecular World
Do not set off a clause that is essential to the sentence. Such clauses often begin with that.
Systematic surveys of the ocean floor revealed, that
there were submarine mountain ranges, that extended for
thousands of kilometers.
Systematic surveys of the ocean floor revealed that
there were submarine mountain ranges that extended for
thousands of kilometers.
Do not use a comma to separate the subject from the rest of the sentence.
A biosensor that produces a changing electrical signal in
response to levels of glucose in the bloodstream of diabetics, could be
used to control the release of insulin so as to maintain the concentration of
blood sugar at a steady, safe level.
A biosensor that produces a changing electrical signal in
response to levels of glucose in the bloodstream of diabetics could be
used to control the release of insulin so as to maintain the concentration of
blood sugar at a steady, safe level.
--Adapted from Philip Ball, Designing the Molecular World