1. Some parameters of speech sound production

Voicing
As air flows from the lungs to the mouth and nose, it passes through the larynx ("voice box") where the glottis ("vocal chords") may be nearly closed and tensed so that the cartilages at the opening vibrate, imposing an audio signal on the air stream. Sounds made without this glottal vibration are said to be voiceless. A good contrast between voiced and voiceless sounds in English is found in the pair lazy and lacy. The z of lazy represents a voiced sound, while the c of lacy represents a voiceless sound. There are no such contrasts in Blackfoot, but voicing is an important feature nevertheless. (See Generalizations for Blackfoot, below.)

Shape of the oral cavity
The quality (timbre) of vowels and semivowels is determined by the complex patterns of the audio signal carried by the air flow leaving the mouth. As stated above, an audio signal is imposed on the air flow as it passes through the larynx. The oral cavity acts as a filter which more readily passes certain harmonics of this audio signal; the shape of the oral cavity determines which harmonics are passed and which are attenuated. The primary determinant for the shape of the oral cavity is the position of the tongue. It is common to describe vowels with respect to the location of the highest point on the tongue. For example, the vowel of English me is produced with the blade of the tongue high and to the front of the mouth, so it is described as a high, front vowel. Blackfoot has the following vowels: high front [i], low front [æ], low central [a], mid to high back [o], and low back (which I will represent here as [O]). These are similar to English vowels as follows: [i] is like the vowel of English she; the vowel [æ] is that of English at; [a] is the first vowel of father; Blackfoot [o] is about half way between the vowels of go and do, and like those vowels, involves lip rounding; Blackfoot [O] is rounded also; it is like the sound spelled aw in dawn for speakers of English who pronounce this differently than they pronounce don. (This description of these vowels is simplified, in the sense that their basic quality has been described. The vowels [i], [æ], and [a] have predictable variants in well-defined environments, as will be described below under Generalizations for Blackfoot.)

 The shape of the oral cavity is also the determining factor for the quality of semivowels. These are like vowels except for their duration and consequently their position in the syllable: semivowels involve a gliding movement of the tongue into and out of a high front or high back position. They are never the nucleus of syllables, always occuring next to vowels. Blackfoot has a high front semivowel [y] and a high back semivowel [w]. Like the back vowel [o], the lips are rounded for [w].

Point of air flow constriction in the mouth.
The description of consonants makes reference to the point in the mouth where the air flow is constricted, such as at the lips, or at various points along the roof of the mouth as the tongue touches it. These points are sometimes referred to as "points of articulation". The important points for Blackfoot are the lips, alveolar ridge (behind the teeth), the front portion of the palate, and the velum ("soft palate"). Consonants articulated at these points are described as labial, alveolar, palatal, and velar, respectively.

Degree of air flow constriction in the mouth.
Air flow in the mouth may be completely blocked, as in stops and nasals (see below), or constricted to the extent that the air being forced through makes a noise; the latter sounds are called fricatives. Vowels (see above) are produced with virtually no constriction in the mouth.

Velic status (open or closed)
The velic is a valve at the back of the roof of the mouth. It may be open, allowing air to flow through the nasal passage, or closed.

Glottis as a valve
Blackfoot uses the glottis as an additional point of constriction; as we will see, a complete closure after a vowel counts as a consonant.

2. Classes of consonants

 It is useful to recognize groups of sounds which have features in common, because this allows us to make generalizations about those groups, as we will see just below and later when describing phonological rules.

 Stops:
When there is complete blockage of air flow in the mouth and the velic is closed so no air can escape through the nasal passage, then as soon as the air pressure in the mouth matches the air pressure from the lungs, air flow completely stops. E.g., if the lips are closed and the velic is closed, the air flow is halted as pressure builds up behind the lips. The resulting consonant is called a labial stop. Blackfoot has labial [p], alveolar [t], and velar [k] stops. A constriction at the glottis (represented here as [?]) is also considered a stop (glottal stop), even though the closure is not in the mouth.

 Nasals:
If there is an oral closure but the velic remains open, then the entire air flow will be via the nasal passage. The point of closure in the mouth is still significant, however, because shape of the oral cavity will affect the quality (timbre) of the sound as it does for vowels (see below), especially if they are voiced, as they almost always are. Blackfoot has labial [m] and alveolar [n] nasals.

 Fricatives:
The oral closure is not complete, and air being forced through produces noise. The velic is closed, else the pressure in the mouth could not be great enough to force air through the oral constriction. Blackfoot has an alveolar fricative [s], about like the sound represented by s in English horse. Blackfoot also has a velar fricative [x]; it is about like the sound usually represented by ch in German.

 Affricates:
If the closure for a stop is not opened abruptly and completely, but rather the closure is only partially opened so as to allow air to pass through with difficulty, then the release will be heard as a fricative. The resulting complex sound is called an affricate. Blackfoot has two affricates. One [ts] is at the alveolar ridge, and sounds about like the ts in the word cats. The other affricate [ks] begins with a velar closure, but during the release there is a partial closure at the alveolar ridge, so that it sounds similar to the sound written x in the English word box.

3. Definitions:
stop = air flow blocked (glottal closure, or oral closure with velic closed)
nasal= oral closure & velic open
fricative = friction noise as air flows through a constriction & velic closed
affricate = stop with fricative release
vowel = sound produced by resonance within the oral cavity; occurs as the nucleus of a syllable
semivowel = glide of tongue into a high front or back position; occurs as part of a syllable margin

4. Generalizations for Blackfoot:
Stops, fricatives, and the affricates are voiceless and unaspirated.
Nasals are voiced.
Vowels are voiced and non-nasalized (i.e., the velic is closed).
Semivowels are voiced and non-nasalized.

 Predictable variation:
[a] is higher (central) if it is both short and followed by a long consonant.
[i] is lax if it is both short and in a closed syllable.
[æ] is higher and tense (like French é) when it precedes a [?], higher and lax (like the e of English  bet) if it is in a closed syllable, and is long otherwise.
[o] is usually higher and lax (like the vowel of English put) before a long consonant.
Unaccented vowels are usually voiceless at the end of a word.
Velar consonants ([x,k,ks]) are palatal if immediately preceded by a front vowel.

5. Non-English distinctions in Blackfoot

 Accent
Blackfoot has a non-predictable pitch accent. That is, every polysyllabic Blackfoot word has at least one syllable with distinctively high pitch.

Vowel length
Blackfoot vowels are either long or short, and this length is distinctive.

Consonant length
All Blackfoot consonants except [x] and [?] are either long or short, and this length is distinctive.

Other Contrasts with English:
Much less aspiration of stops in Blackfoot, if any, than in English.
Blackfoot [o] is not glided.