Aspiration of p, t, k in English

Question

I'm trying to figure out when exactly p, t, k should be aspirated in (American) English.

Here's what I found here:

• Voiceless stops are aspirated at the beginning of a word, and at the beginning of a stressed syllable.

• Voiceless stops are unaspirated at the beginning of an unstressed syllable. They’re also unaspirated in any other position, like at the end of a syllable or the end of a word.

• And even if a syllable is stressed, a voiceless stop is unaspirated if it follows [s].

• In English, voiced stops are never aspirated. They’re always unaspirated.

Don't the first two bullet points contradict each other? The first says that voiceless stops are aspirated at the beginning of the word, but the second says that they are unaspirated at the beginning of the word if this syllable is unstressed.

Further, I found this:

Where an English speaker does and doesn't use aspiration is predictable. For most English dialects, the two environments where voiceless plosives are aspirated are:

• At the beginning of a stressed syllable. (The [k] of skill isn't at the beginning of the syllable -- there's a [s] before it.)
• At the beginning of a word -- whether the syllable is stressed or not.

In potato, the p will be aspirated because it is at the beginning of the word and t will be aspirated because it's at the beginning of a stressed syllable: [pʰəˈtʰeɾo].

The second bullet points in this source agrees with the first one of the previous source (but also contradicts "Voiceless stops are unaspirated at the beginning of an unstressed syllable"). So which description is most accurate? If neither of these two is accurate, what's ""the proper" description?

Answer 1

I think the confusion comes from not also having rules assigning non-aspiration – which we don't do. If you assume that sops are basically unaspirated and then require rules that only specify where they become aspirated, there is no problem. Hence there can be two rules assigning aspiration – word-initially, and at the beginning of a stressed syllable – and no necessity of ordering the rules.

The first description attempts to explicitly predict both values. The rule "Voiceless stops are unaspirated at the beginning of an unstressed syllable" is unnecessary. Once you say where things are aspirated, you can simply say "unaspirated in any other position", and it you say that stops are by over-rideable nature unaspirated, you don't have to have rule that makes stops be unaspirated. The second description assumes that you only say where things change, i.e. become aspirated.

Answer 2

There is no contradiction. As written, Rule 1 supersedes rule 2.

1. Aspirate at the beginning of words, regardless of stress.
2. Aspirate at the beginning of stressed syllables, in any position.

It is a mistake to think of aspiration as a forceful breath in English. It is a delay in the onset of voicing. A 60-80 ms long whisper of the following vowel, W, R or L. Compared to other languages, English aspiration has a fairly long VOT or “voice onset time,” but not the exhalation of heavy breath used in some other languages. To grasp VOT, try whispering the word Doe, then tack on voiced Oh. (doe)-OH is closer to English Toe than toe-HOE.

Similarly, most who try to resurrect the moribund wh mistakenly pronounce the exaggerated sequence h-w. But when it still existed in the vernacular, wh was the single, quick sound of a voiceless w, whispered but with no h or special puff of breath.