2nd to 3rd base. From kissing to petting or the inverse? Having never played baseball, I haven't a clue. But having studied classical clarinet at the conservatory, I know a bit about music. In very broad strokes, it distinguishes between two textures, legato and staccato. When two notes are to be played legato, the score shows them connected by an arc. When they're to be played staccato, they're topped by dots. The most extreme type of legato is a piano scale played with disengaged damper pedal. Each tone runs into the next. Because none are stopped, their bloom/fade portions overlay like a cluster or chord. Sterling staccato examples are a trumpet repeating the same tone sharply tongued like in a military fanfare; or a rapidly picked flamenco guitar arpeggio played nails on steel strings to sound hyper clipped and articulated.

Legato connects, staccato separates. Legato has no breaks, staccato must have. Woodwind and brasses use tonguing to interrupt airflow and separate tones. Strings get picked, slapped or 'hacked' by bow. Percussion is mostly staccato because its main noise makers are highly damped then struck. We talk of a bass drum's kick or a snare drum's hit. Cymbals ringing out are an exception and when tickled softly with a brush, can assume legato qualities. In the time domain, legato is softer and more ambiguous because the start of each tone isn't as sharply focused. It's drawn with a softer-tipped pencil. Staccato is hard and very specific. Now degrees mellow these distinctions. Staccato can be played extra hard with maximal damping to make each tone ultra short. A common street example is the road-construction jack hammer. But staccato can also be soft. Now each individual tone starts and ends more gently. Compare La-La-La to Ta-Ta-Ta. Either way your tongue will interrupt airflow to separate vowel from consonant but 'L' has a softer beginning than 'T'. Da-Da-Da is still sharper than La-La-La but already softer than Ta-Ta-Ta. 50 shades of grey. How about Blah-Blah-Blah? Staccato shows clean oil/acrylic separation, legato more watercolor transitions.

Now we can make intuitive sense of Nelson's 2nd-order/3rd-order dominant THD descriptions. We simply connect them to legato/staccato respectively. Everything else being equal—which of course it never is—a circuit with dominant 2nd-order harmonic distortion will sound softer or less enunciated than one whose 3rd harmonic dominates. The relative amount of this distortion creates higher/lower degrees of the effect. Someone speaking in continuous sing-song to run each syllable into the next because of a very lazy tongue represents 'deep triode' aka high 2nd-order THD. Someone speaking most clipped and hyper enunciated represents the overdone 3rd-order feel. The second harmonic occurs an octave above its fundamental so C2 over C1. The third octave sits an octave plus fifth above the fundamental so G2 over C1. The 4th harmonic is C3 above C1. As harmonics increase their order, the relationship to the fundamental becomes less harmonious. Now ever milder doses of ever higher orders rub far more than higher doses of lower-order distortion which still belong. In Jazz, the minor 3rd and minor 7th are the classic blue notes whose friction within a major chord create the genre's recognizable 'modern' tonality. Blue notes don't blend. They stand out. The higher the order of harmonic distortion becomes, the bluer or more dissonant their effect. If the octave doubling of 2nd/4th-order THD is honey, the 3rd harmonic is salt, the higher uneven harmonics become paprika then chili pepper. The 7th in particular bites.

In hifi circuits, the 2nd harmonic is called most innocuous because in low doses, it's perfectly hidden. Try it. Have a woman sing the same tone as you. It'll naturally be an octave higher. If her pitch is accurate, she'll simply reinforce you. The more softly she sings, the harder it gets to make her out as a separate entity. Two octaves blend perfectly together. You'll simply sound a bit richer and somewhat enhanced over your usual solo self. If she instead sings the open fifth to represent the 3rd harmonic, her otherness increases. She's heard as a separate though still harmonious contributor. Compared to octave doubling, that remains true for longer as her power versus that of your fundamental diminishes. That's back to legato's connectivity/blending versus staccato's separation.