No Transitive Closure for Suffix Rules

There is no transitive closure for suffix rules. If you had a suffix rule for building, say, a .Y file from a .X file, and another for building a .Z file from a .Y file, make would not combine their rules to build a .Z file from a .X file. You must specify the intermediate steps as targets, although their entries can have null rules:

trans.Z: 
trans.Y:

In this example trans.Z is built from trans.Y if it exists. Without the appearance of trans.Y as a target entry, make might fail with a "don't know how to build" error, since there would be no dependency file to use. The target entry for trans.Y guarantees that make will attempt to build it when it is out of date or missing. Since no rule is supplied in the makefile, make will use the appropriate implicit rule, which in this case would be the .X.Y rule. If trans.X exists (or can be retrieved from SCCS), make rebuilds both trans.Y and trans.Z as needed.