AOS and expressive aphasia (also known as Broca's aphasia) are commonly mistaken as the same disorder mainly because they often occur together in patients. Although both disorders present with symptoms such as a difficulty producing sounds due to damage in the language parts of the brain, they are not the same. The main difference between these disorders lies in the ability to comprehend spoken language; patients with apraxia are able to fully comprehend speech, while patients with aphasia are not always fully able to comprehend others' speech.

Conduction aphasia is another speech disorder that is similar to, but not the same as, apraxia of speech. Although patients who suffer from conduction aphasia have full comprehension of speech, as do AOS sufferers, there are differences between the two disorders. Patients with conduction aphasia are typically able to speak fluently, but they do not have the ability to repeat what they hear.

Similarly, dysarthria, another motor speech disorder, is characterized by difficulty articulating sounds. The difficulty in articulation does not occur due in planning the motor movement, as happens with AOS. Instead, dysarthria is caused by inability in or weakness of the muscles in the mouth, face, and respiratory system.

There are three significant features that differentiate DVD/CAS from other childhood speech sound disorders. These features are:

- "Inconsistent errors on consonants and vowels in repeated productions of syllables and words

- Lengthened coarticulatory transitions between sounds and syllables

- Inappropriate prosody, especially in the realization of lexical or phrasal stress"

Even though DVD/CAS is a "developmental" disorder, it will not simply disappear when children grow older. Children with this disorder do not follow typical patterns of language acquisition and will need treatment in order to make progress.

The warning signs of early speech delay are categorized into age related milestones, beginning at the age of 12 months and continuing through early adolescence.

At the age of 12 months, there is cause for concern if the child is not able to do the following:

- Using gestures such as waving good-bye and pointing at objects

- Practicing the use of several different consonant sounds

- Vocalizing or communicating needs

Between the ages of 15 and 18 months children are at a higher risk for speech delay if they are displaying the following:

- Not saying "momma" and "dada"

- Not reciprocating when told "no", "hello", and "bye"

- Does not have a one to three word vocabulary at 12 months and up to 15 words by 18 months

- Is unable to identify body parts

- Displaying difficulties imitating sounds and actions

- Shows preference to gestures over verbalization

Additional signs of speech delay after the age of 2 years and up to the age of 4 include the following:

- Inability to spontaneously produce words and phrases

- Inability to follow simple directions and commands

- Cannot make two word connections

- Lacks consonant sounds at the beginning or end of words

- Is difficult to understand by close family members

- Is not able to display the tasks of common household objects

- Is unable to form simple 2 to 3 word sentences

Primary stuttering behaviors are the overt, observable signs of speech disfluencies, including repeating sounds, syllables, words or phrases, silent blocks and prolongation of sounds. These differ from the normal dysfluencies found in all speakers in that stuttering dysfluencies may last longer, occur more frequently, and are produced with more effort and strain. Stuttering dysfluencies also vary in quality: common dysfluencies tend to be repeated movements, fixed postures, or superfluous behaviors. Each of these three categories is composed of subgroups of stutters and dysfluencies.

- Repeated movements

- Part-word repetition—a single segment of a word is repeated (for example: "s-s-stuttering!") or a part of a word which is still a full syllable such as "un—un—under the..." and "o—o—open".

- Incomplete syllable repetition—an incomplete syllable is repeated, such as a consonant without a vowel, for example, "c—c—c—cold".

- Whole-word repetition—a whole word, or more than one word is repeated, such as "I know—I know—I know a lot of information.".

- Fixed postures

- Prolongation—prolongation of a sound occurs such as "mmmmmmmmmom".

- Block—such as a block of speech or a tense pause where nothing is said despite efforts.

- Superfluous behaviors

- Interjections—this includes an interjection such as an unnecessary "uh" or "um" as well as revisions, such as going back and correcting one's initial statements such as "I—My girlfriend...", where the "I" has been corrected to the word "my".

- Secondary characteristics—these are visible or audible speech behaviors, such as lip smacking, throat clearing, head thrusting, etc., usually representing an effort to break through or circumvent a block or stuttering loop.

Apraxia of speech (AOS) is an acquired oral motor speech disorder affecting an individual's ability to translate conscious speech plans into motor plans, which results in limited and difficult speech ability. By the definition of apraxia, AOS affects volitional (willful or purposeful) movement patterns, however AOS usually also affects automatic speech.

Individuals with AOS have difficulty connecting speech messages from the brain to the mouth. AOS is a loss of prior speech ability resulting from a brain injury such as a stroke or progressive illness.

Developmental verbal dyspraxia (DVD), also known as childhood apraxia of speech (CAS) and developmental apraxia of speech (DAS); is an inability to utilize motor planning to perform movements necessary for speech during a child's language learning process. Although the causes differ between AOS and DVD, the main characteristics and treatments are similar.

Speech and language impairment are basic categories that might be drawn in issues of communication involve hearing, speech, language, and fluency.

A speech impairment is characterized by difficulty in articulation of words. Examples include stuttering or problems producing particular sounds. Articulation refers to the sounds, syllables, and phonology produced by the individual. Voice, however, may refer to the characteristics of the sounds produced—specifically, the pitch, quality, and intensity of the sound. Often, fluency will also be considered a category under speech, encompassing the characteristics of rhythm, rate, and emphasis of the sound produced

A language impairment is a specific impairment in understanding and sharing thoughts and ideas, i.e. a disorder that involves the processing of linguistic information. Problems that may be experienced can involve the form of language, including grammar, morphology, syntax; and the functional aspects of language, including semantics and pragmatics

An individual can have one or both types of impairment. These impairments/disorders are identified by a speech and language pathologist.

Even though most speech sound disorders can be successfully treated in childhood, and a few may even outgrow them on their own, errors may sometimes persist into adulthood rather than only being not age appropriate. Such persisting errors are referred to as "residual errors" and may remain for life.

Stuttering, also known as stammering, is a speech disorder in which the flow of speech is disrupted by involuntary repetitions and prolongations of sounds, syllables, words or phrases as well as involuntary silent pauses or blocks in which the person who stutters is unable to produce sounds. The term "stuttering" is most commonly associated with involuntary sound repetition, but it also encompasses the abnormal hesitation or pausing before speech, referred to by people who stutter as "blocks", and the prolongation of certain sounds, usually vowels or semivowels. According to Watkins et al., stuttering is a disorder of "selection, initiation, and execution of motor sequences necessary for fluent speech production." For many people who stutter, repetition is the primary problem. The term "stuttering" covers a wide range of severity, encompassing barely perceptible impediments that are largely cosmetic to severe symptoms that effectively prevent oral communication. In the world, approximately four times as many men as women stutter, encompassing 70 million people worldwide, or about 1% of the world's population.

The impact of stuttering on a person's functioning and emotional state can be severe. This may include fears of having to enunciate specific vowels or consonants, fears of being caught stuttering in social situations, self-imposed isolation, anxiety, stress, shame, being a possible target of bullying (especially in children), having to use word substitution and rearrange words in a sentence to hide stuttering, or a feeling of "loss of control" during speech. Stuttering is sometimes popularly seen as a symptom of anxiety, but there is actually no direct correlation in that direction (though as mentioned the inverse can be true, as social anxiety may actually develop in individuals as a result of their stuttering).

Stuttering is generally not a problem with the physical production of speech sounds or putting thoughts into words. Acute nervousness and stress do not cause stuttering, but they can trigger stuttering in people who have the speech disorder, and living with a stigmatized disability can result in anxiety and high allostatic stress load (chronic nervousness and stress) that reduce the amount of acute stress necessary to trigger stuttering in any given person who stutters, exacerbating the problem in the manner of a positive feedback system; the name 'stuttered speech syndrome' has been proposed for this condition. Neither acute nor chronic stress, however, itself creates any predisposition to stuttering.

The disorder is also "variable", which means that in certain situations, such as talking on the telephone or in a large group, the stuttering might be more severe or less, depending on whether or not the stutterer is self-conscious about their stuttering. Stutterers often find that their stuttering fluctuates and that they have "good" days, "bad" days and "stutter-free" days. The times in which their stuttering fluctuates can be random. Although the exact etiology, or cause, of stuttering is unknown, both genetics and neurophysiology are thought to contribute. There are many treatments and speech therapy techniques available that may help decrease speech disfluency in some people who stutter to the point where an untrained ear cannot identify a problem; however, there is essentially no cure for the disorder at present. The severity of the person's stuttering would correspond to the amount of speech therapy needed to decrease disfluency. For severe stuttering, long-term therapy and hard work is required to decrease disfluency.

Selective mutism previously known as "elective mutism" is an anxiety disorder very common among young children, characterized by the inability to speak in certain situations. It should not to be confused with someone who is mute and cannot communicate due to physical disabilities. Selectively mute children are able to communicate in situations in which they feel comfortable. About 90% of children with this disorder have also been diagnosed with social anxiety. It is very common for symptoms to occur before the age of five and do not have a set time period. Not all children express the same symptoms. Some may stand motionless and freeze in specific social settings and have no communication.

Alalia is a disorder that refers to a delay in the development of speaking abilities in children. In severe cases, some children never learn how to speak. It is caused by illness of the child or the parents, the general disorders of the muscles, the shyness of the child or that the parents are close relatives.

Anarthria is a severe form of dysarthria. The coordination of movements of the mouth and tongue or the conscious coordination of the lungs are damaged.

Aphasia can rob all aspects of the speech and language. It is a damage of the cerebral centres of the language.

Aphonia is the inability to produce any voice. In severe cases the patient loses phonation. It is caused by the injury, paralysis, and illness of the larynx.

Conversion disorder can cause loss of speaking ability.

Feral children grow up outside of human society, and so usually struggle in learning any language.

Some people with autism never learn to speak.

Most intellectually disabled children learn to speak, but in the severe cases they can't learn speech (IQ 20-25). Children with Williams syndrome have good language skills with mean IQ 50. Children with Down syndrome often have impaired language and speech.

Language disorders or language impairments are disorders that involve the processing of linguistic information. Problems that may be experienced can involve grammar (syntax and/or morphology), semantics (meaning), or other aspects of language. These problems may be receptive (involving impaired language comprehension), expressive (involving language production), or a combination of both. Examples include specific language impairment and aphasia, among others. Language disorders can affect both spoken and written language, and can also affect sign language; typically, all forms of language will be impaired.

Current data indicates that 7% of young children display language disorder, with boys being diagnosed twice as much as girls.

Preliminary research on potential risk factors have suggested biological components, such as low-birth weight, prematurity, general birth complications, and male gender, as well as family history and low parental education can increase the chance of developing language disorders.

For children with phonological and expressive language difficulties, there is evidence supporting speech and language therapy. However, the same therapy is shown to be much less effective for receptive language difficulties. These results are consistent with the poorer prognosis for receptive language impairments that are generally accompanied with problems in reading comprehension.

Note that these are distinct from speech disorders, which involve difficulty with the act of speech production, but not with language.

Language disorders tend to manifest in two different ways: receptive language disorders (where one cannot properly comprehend language) and expressive language disorders (where one cannot properly communicate their intended message).

Speech delay, also known as alalia, refers to a delay in the development or use of the mechanisms that produce speech. Speech, as distinct from language, refers to the actual process of making sounds, using such organs and structures as the lungs, vocal cords, mouth, tongue, teeth, etc. Language delay refers to a delay in the development or use of the knowledge of language.

Because language and speech are two independent stages, they may be individually delayed. For example, a child may be delayed in speech (i.e., unable to produce intelligible speech sounds), but not delayed in language. In this case, the child would be attempting to produce an age appropriate amount of language, but that language would be difficult or impossible to understand. Conversely, since a child with a language delay typically has not yet had the opportunity to produce speech sounds, it is likely to have a delay in speech as well.

In some cases phonetic and phonemic errors may coexist in the same person. In such case the primary focus is usually on the phonological component but articulation therapy may be needed as part of the process, since teaching a child how to use a sound is not practical if the child does not know how to produce it.

Expressive language disorder is a communication disorder in which there are difficulties with verbal and written expression. It is a specific language impairment characterized by an ability to use expressive spoken language that is markedly below the appropriate level for the mental age, but with a language comprehension that is within normal limits. There can be problems with vocabulary, producing complex sentences, and remembering words, and there may or may not be abnormalities in articulation.

As well as present speech production, very often, someone will have difficulty remembering things. This memory problem is only disturbing for speech; non-verbal or non-linguistically based memory will be unimpaired. An example of a child with expressive language disorder can be seen here.

Expressive language disorder affects work and schooling in many ways. It is usually treated by specific speech therapy, and usually cannot be expected to go away on its own.

Expressive language disorder can be further classified into two groups: developmental expressive language disorder and acquired expressive language disorder. Developmental expressive language disorder currently has no known cause, is first observed when a child is learning to talk, is more common in boys than girls, and is much more common than the acquired form of the disorder. Acquired expressive language disorder is caused by specific damage to the brain by a stroke, traumatic brain injury, or seizures.

Care must be taken to distinguish expressive language disorder from other communication disorders, sensory-motor disturbances, intellectual disability and/or environmental deprivation (see DSM-IV-TR criterion D). These factors affect a person's speech and writing to certain predictable extents, and with certain differences.

Careful diagnosis is also important because "atypical language development can be a secondary characteristic of other physical and developmental problems that may first manifest as language problems".

Speech disorders or speech impediments are a type of communication disorder where 'normal' speech is disrupted. This can mean stuttering, lisps, etc. Someone who is unable to speak due to a speech disorder is considered mute.

In psychiatry, stilted speech or pedantic speech is communication characterized by situationally inappropriate formality. This formality can be expressed both through abnormal prosody as well as speech content that is "inappropriately pompous, legalistic, philosophical, or quaint". Often, such speech can act as evidence for autism spectrum disorder (ASD) or a thought disorder, a common symptom in schizophrenia or schizotypal personality disorder.

To diagnose stilted speech, researchers have previously looked for the following characteristics:

- speech conveying more information than necessary

- vocabulary and grammar expected from formal writing rather than conversational speech

- unneeded repetition or corrections

While literal and long-winded word content is often the most identifiable feature of stilted speech, such speech often displays irregular prosody, especially in resonance. Often, the loudness, pitch, rate, and nasality of pedantic speech vary from normal speech, resulting in the perception of pedantic or stilted speaking. For example, overly loud or high-pitched speech can come across to listeners as overly forceful while slow or nasal speech creates an impression of condescension.

These attributions, which are commonly found in patients with ASD, partially account for why stilted speech has been considered a diagnostic criteria for the disorder. Stilted speech, along with atypical intonation, semantic drift, terseness, and perseveration, are all qualities known to be commonly impaired during conversation with adolescents on the autistic spectrum. Often, stilted speech found in children with ASD will also be especially stereotypic or rehearsed.

Patients with schizophrenia are also known to experience stilted speech. This symptom is attributed to both an inability to access more commonly used words and a difficulty understanding pragmatics, or the relationship between language and context. However, stilted speech appears as less common symptom compared to a certain number of other symptoms of the psychosis (Adler "et al" 1999). This element of cognitive disorder is also exhibited as a symptom in the narcissistic personality disorder (Akhtar & Thomson 1982).

In its more common usage, "stilted speech" is a term used to describe overly-formal, unnatural-sounding speech.

Individuals with PLI have particular trouble understanding the meaning of what others are saying, and they are challenged in using language appropriately to get their needs met and interact with others. Children with the disorder often exhibit:

- delayed language development

- aphasic speech (such as word search pauses, jargoning, word order errors, word category errors, verb tense errors)

- Stuttering or cluttering speech

- Repeating words or phrases

- difficulty with pronouns or pronoun reversal

- difficulty understanding questions

- difficulty understanding choices and making decisions.

- difficulty following conversations or stories. Conversations are "off-topic" or "one-sided".

- difficulty extracting the key points from a conversation or story; they tend to get lost in the details

- difficulty with verb tenses

- difficulty explaining or describing an event

- tendency to be concrete or prefer facts to stories

- difficulty understanding satire or jokes

- difficulty understanding contextual cues

- difficulty in reading comprehension

- difficulty with reading body language

- difficulty in making and maintaining friendships and relationships because of delayed language development.

- difficulty in distinguishing offensive remarks

- difficulty with organizational skills

Developmental verbal dyspraxia (DVD), also known as childhood apraxia of speech (CAS) and developmental apraxia of speech (DAS), is when children have problems saying sounds, syllables, and words. This is not because of muscle weakness or paralysis. The brain has problems planning to move the body parts (e.g., lips, jaw, tongue) needed for speech. The child knows what they want to say, but their brain has difficulty coordinating the muscle movements necessary to say those words. The exact cause of this disorder is unknown. Some observations suggest a genetic cause of DVD, as many with the disorder have a family history of communication disorders. There is no cure for DVD, but with appropriate, intensive intervention, people with this motor speech disorder can improve significantly.

Aphasia is loss of the ability to produce or comprehend language. There are acute aphasias which result from stroke or brain injury, and primary progressive aphasias caused by progressive illnesses such as dementia.

- Acute aphasias

- Expressive aphasia also known as Broca's aphasia, expressive aphasia is a non-fluent aphasia that is characterized by damage to the frontal lobe region of the brain. A person with expressive aphasia usually speaks in short sentences that make sense but take great effort to produce. Also, a person with expressive aphasia understands another person's speech but has trouble responding quickly.

- Receptive aphasia also known as Wernicke's aphasia, receptive aphasia is a fluent aphasia that is categorized by damage to the temporal lobe region of the brain. A person with receptive aphasia usually speaks in long sentences that have no meaning or content. People with this type of aphasia often have trouble understanding other's speech and generally do not realize that they are not making any sense.

- Conduction aphasia

- Anomic aphasia

- Global aphasia

- Primary progressive aphasias

- Progressive nonfluent aphasia

- Semantic dementia

- Logopenic progressive aphasia

Given the previously stated signs and symptoms the following behaviors are often seen in people with aphasia as a result of attempted compensation for incurred speech and language deficits:

- Self-repairs: Further disruptions in fluent speech as a result of mis-attempts to repair erred speech production.

- Speech disfluencies: Include previously mentioned disfluencies including repetitions and prolongations at the phonemic, syllable and word level presenting in pathological/ severe levels of frequency.

- Struggle in non-fluent aphasias: A severe increase in expelled effort to speak after a life where talking and communicating was an ability that came so easily can cause visible frustration.

- Preserved and automatic language: A behavior in which some language or language sequences that were used so frequently, prior to onset, they still possess the ability to produce them with more ease than other language post onset.

People with aphasia may experience any of the following behaviors due to an acquired brain injury, although some of these symptoms may be due to related or concomitant problems such as dysarthria or apraxia and not primarily due to aphasia. Aphasia symptoms can vary based on the location of damage in the brain. Signs and symptoms may or may not be present in individuals with aphasia and may vary in severity and level of disruption to communication. Often those with aphasia will try to hide their inability to name objects by using words like "thing". So when asked to name a pencil they may say it is a thing used to write.

- Inability to comprehend language

- Inability to pronounce, not due to muscle paralysis or weakness

- Inability to speak spontaneously

- Inability to form words

- Inability to name objects (anomia)

- Poor enunciation

- Excessive creation and use of personal neologisms

- Inability to repeat a phrase

- Persistent repetition of one syllable, word, or phrase (stereotypies)

- Paraphasia (substituting letters, syllables or words)

- Agrammatism (inability to speak in a grammatically correct fashion)

- Dysprosody (alterations in inflexion, stress, and rhythm)

- Incomplete sentences

- Inability to read

- Inability to write

- Limited verbal output

- Difficulty in naming

- Speech disorder

- Speaking gibberish

- Inability to follow or understand simple requests

Examples of disorders that may include or create challenges in language and communication and/or may co-occur with the above disorders:

- autism spectrum disorder - autistic disorder (also called "classic" autism), pervasive developmental disorder, and Asperger syndrome – developmental disorders that affect the brain's normal development of social and communication skills.

- expressive language disorder – affects speaking and understanding where there is no delay in non-verbal intelligence.

- mixed receptive-expressive language disorder – affects speaking, understanding, reading and writing where there is no delay in non-verbal intelligence.

- specific language impairment – a language disorder that delays the mastery of language skills in children who have no hearing loss or other developmental delays. SLI is also called developmental language disorder, language delay, or developmental dysphasia.

The following are brief definitions of several of the more prominent speech disorders:

Classifying speech into normal and disordered is more problematic than it first seems. By a strict classification, only 5% to 10% of the population has a completely normal manner of speaking (with respect to all parameters) and healthy voice; all others suffer from one disorder or another.

There are three different levels of classification when determining the magnitude and type of a speech disorders and the proper treatment or therapy:

1. Sounds the patient can produce

1. Phonemic – can be produced easily; used meaningfully and constructively

2. Phonetic – produced only upon request; not used consistently, meaningfully, or constructively; not used in connected speech

2. Stimulate sounds

1. Easily stimulated

2. Stimulate after demonstration and probing (i.e. with a tongue depressor)

3. Cannot produce the sound

1. Cannot be produced voluntarily

2. No production ever observed

Those who are physically mute may have problems with the parts of the human body required for human speech (the esophagus, vocal cords, lungs, mouth, or tongue, etc.).

Trauma or injury to Broca's area, located in the left inferior frontal cortex of the brain, can cause muteness.

Receptive language disorders can be acquired or developmental (most often the latter). When developmental, difficulties in spoken language tend to occur before three years of age. Usually such disorders are accompanied by expressive language disorders.

However, unique symptoms and signs of a receptive language disorder include: struggling to understand meanings of words and sentences, struggling to put words in proper order, and inability to follow verbal instruction.

Treatment options include: language therapy, special education classes for children at school, and a psychologist if accompanying behavioral problems are present.