Empty Set Therapy 

Empty Set Therapy: Empty Set is a linguistic method of speech therapy that involves a child learning two new sounds concurrently that are maximally different in terms of place, manner and voice.

The term Empty Set, or null set, is borrowed from a mathematical theory where a unique set has no elements. In case of numbers, 6, 8 and 4 exist as separate entities but are considered a set of three

Similarly, in empty set speech therapy, a child is introduced to two new sounds neither of which the child is able to produce independently nor when following a clinician's model. The expectation of empty set therapy is that the child will have a much better chance of generalizing non-stimulable sounds that are linguistically complex and maximally distinct rather than sounds that are homonymous, as targeted in minimal pair therapy.

With treatment of the empty set, the two target sounds selected are consonant phonemes that are maximally different from the other. That is, for best results, the sounds are maximally different in voice, manner, place and major class.

Major class refers to whether the sounds being contrasted are obstruents or sonorants. Follow the link to the Minimal Pairs Therapy page for more information about major class distinctions such as obstruents and sonorants.

What does Empty Set Treatment look like?

Treatment of the Empty Set is thought to be most beneficial for children who have moderate to severe phonological disorder. Empty Set therapy involves selecting and contrasting 2 phonemes that are not yet part of a child's phonetic inventory. In other words, 2 consonant sounds are selected as speech therapy targets that a child is not stimulable for. 

In our example, Peter, age 5, is unable to produce the speech sound /p/. Peter is also unable to produce the speech sound /l/. Now, because the two target sounds are maximally opposite and because Peter is unable to produce either sound, the two sounds would be considered as ideal targets for Empty Set therapy. 

Empty Set Treatment Seems Counter-Intuitive

Target selection for Empty Set is difficult to conceptualize because it seems so counter-intuitive. How does it benefit a child with severe phonological disorder to learn 2 sounds during a session, neither of which the child is stimulable for? To understand the rationale for target selection it's important we spend some time discussing learnability theory.

This is a simplified explanation, but learnability theory contends that when a child learns the complexity of a language system, he/she will be better placed to learn different aspects of that system. This will enable the child to understand the rules and varied fragments of a language system.

In terms of the phonological system, a child who is introduced to and learns complex speech sounds - importantly, and this is key, that are beyond his current knowledge - then his/her understanding of the phonological system as a whole will be enhanced. This should lead to more rapid learning of the phonological system, which goes well beyond just the two sounds targeted for a particular intervention.  

Minimal Versus Maximal Targets Explained

Minimal pairs treatment enhances a child's ability to distinguish between pairs of words. In minimal pairs therapy, the paired words differ by a single phoneme. For example, /t/ is contrasted with /d/ as found in the paired words tie - dye. The paired phonemes are minimal because /t and /d/ have only a single feature difference, the /t/ is voiceless whereas the /d/ is voiced

The /t/ and /d/ speech sounds are both obstruents and alveolar stops. So in terms of major class, place and manner they are almost the same sound.

Similarly, with our contrast selection for Peter, the targeted words will be paired, and will differ by a single phoneme.

In contrast, however, the /p/ phoneme and the /l/ phoneme feature maximal contrasts, not minimal.

Firstly, the /p/ and /l/ phonemes differ in respect to major class - the /p/ is an obstruent, the /l/ is a sonorant. Second, the paired phonemes also differ in terms of manner, the /p/ is a stop, whereas the /l/ is a liquid. In addition, the /p/ is a voiceless bilabial while the /l/ phoneme is a voiced alveolar

Empty Set Therapy Session

  1. Prior to beginning empty set therapy we make a series of flash cards that target the paired phonemes. The cards have been made following selection based on Caroline Bowen's minimal pairs word lists.
  2. The paired words are pick/lick, pine/line, pot/lot, peg/leg, pop/lop. Note that the target phonemes /p/ and /l/ are in initial position. A selection of pictures from clip-art  are used to make the flash cards.
  3. Peter produces /t/ for /p/, so pick becomes tick.  Peter also produces /w/ for /l/, so line becomes wine.
  4. The therapy session for today will concentrate on imitation of the target sounds, /p/ and /l/. 
  5. The clinician engages Peter's full attention by sitting across from him and explaining that today he is going to learn 2 new sounds. The sounds are /p/ and /l/. The clinician produces these sounds clearly and with emphasis on the articulators and may use a visual cue for each sound such as found in cued articulation.
  6. The clinician then presents the series of previously made flash cards emphasizing the correct production of the initial phoneme. For instance, the clinician holds the card for pick and says pick with emphasis on /p/. This is immediately followed by the card for lick. Again, emphasis is given for correct placement of the tongue for /l/.
  7. Peter is encouraged to attempt the two words pick and lick, and feedback and praise is given for the attempt, even though at this early stage it is unlikely Peter will produce accurate /p/ and /l/, but this is ok. The clinician then moves onto the next word pair pine/line and repeats the process and so on...


Barlow, J.A. and Gierut J.A. (2002) Minimal Pair Approaches to Phonological Remediation Seminars in Speech and Language, Volume 23, No 1

Bowen, C. (Updated 26, Jan, 2013) Word Lists: Minimal Pairs. Retrieved from: http://speech-language-therapy.com 

Bowen, C. (2009) Children's Speech Sound Disorders Wiley-Blackwell

Gierut, J.A. (1989) Maximal Opposition Approach to Phonological Treatment Journal of Speech and Hearing Disorders, Volume 54, 9-19.

Williams, A.L. McLeod, S. & McCauley R.J. (2010) Interventions for Speech Sound Disorders in Children Paul H Brookes Publishing Co  

Williams, A.L. (2006) SCIP Sound Contrasts in Phonology: Evidence Based Treatment Program. User Manual Super Duper Publications

Updated: 07/2014

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