Question: Is there a difference between modality and therapy?

Answer:
Short answer, YES

Modalities are defined as “Any physical agent applied to produce therapeutic changes to biologic tissues; includes but not limited to thermal, acoustic, light, mechanical, or electric energy.” They can be attended OR non-attended.
The definition of modalities was added to CPT 1995 to indicate the different types of service included in this section. To clarify the work performed by the provider, the section is divided into two parts; Supervised and Constant Attendance. Supervised modalities are defined as the application of a modality that does not require direct (one on one) patient contact by the provider. Constant Attendance is defined as the application of a modality that requires direct (one on one) patient contact by the provider.

Therapies are defined as “A manner of effecting change through the application of clinical skills and/or services that attempt to improve function.” These require direct patient contact.
The definition of therapeutic procedures was added to CPT 1995 to clarify the differences between therapeutic procedures, modalities, and tests and measurements. These procedures require direct one on one patient contact by a physician or therapist.

Therapies is kind of general term used by many people to describe all physical medicine procedures — modalities, therapeutic procedures, acupuncture, and sometimes, even CMT.