New Rule vs. Dependency List

[Charles Gerlach]

I don't understand why adding a path forces GNUmake to see
a dependency list as a rule. If I have:

obj.o : obj.f90 dep1 dep2 dep3
#No Tab, no rule.

Then GNUmake recognizes that this is strictly a dependency
list, and uses the pattern rule that I wrote to compile
the object into the directory from which I ran make.

I want the .o file to live in directory $(DIR), so I
modify the dependency list:

$(DIR)/obj.o : obj.f90 dep1 dep2 dep3
#No Tab, no rule.

Now when $(DIR)/obj.o does not exist, GNUmake checks to see
that the dependencies are up to date, but does nothing if
they are. It does not apply the pattern rule. I belive it
thinks that I'm now writing a new rule, and then assumes that
rule is null since I don't have anything specified.

Can anyone tell me 1. why this is, and 2. can I get around it?

Thanks.

-Charles Gerlach