pretty
The history of the word is straightforward, in a twisty sort of way.
The earliest meaning listed in the OED is as follows:
ADJECTIVE
1.a. Old English–
Originally: cunning, crafty. Subsequently: clever, skilful, able.
So it's not surprising that the "clever" shade of meaning led to the next identified meanings:
1.b. c1450–
Cleverly or elegantly made or done; ingenious, artful, well-conceived.
2.a. 1440–
Of a person, esp. a woman or child: attractive and pleasing in appearance; good-looking, esp. in a delicate or diminutive way.
New English Dictionary (OED first edition) (1908) has the following comment: ‘Pretty is somewhat of a condescending term; we grant it: beauty is imperious, and commands our acknowledgement
The hints of negativity are greater in subsequent meanings:
2.c. a1450–
In collocation with little. Frequently depreciative.
1996 We don't need to bother our pretty little heads about it.
Guardian 16 March (Weekend Supplement) 44/3
3.c. 1533–
ironic. Awkward, difficult, deplorable, unwelcome, etc. Cf. fine adj. A.II.7c.
pretty pass: see pass n.3 3. pretty kettle of fish: see kettle n. 2b.
The etymological discussion shows the same ambivalence:
< prat n.1 + ‑y suffix1. Compare Dutch prettig pleasant, nice, agreeable, comfortable (also Belgian Dutch †pruttig), German regional (Low German: East Friesland) prettig sportive, funny, humorous, Old Norwegian prettugr tricky, deceitful (compare Old Icelandic prettóttr), also (with metathesis) Middle Dutch pertich cunning, quick, lively (Dutch regional (southern) pertig, Belgian Dutch pertig, also in sense ‘whimsical, capricious’)
We can be pretty sure that the postive shades of meaning that are commonly used play into its adverbial use:
1.a. 1565–
Qualifying an adjective or adverb: to a considerable extent; fairly, moderately; rather, quite. In later use also: very.
1.b. 1682–
pretty much: almost, very nearly; more or less; (also, in early use) very much, considerably.
nice
The history of this word is quite different. The positive senses popular today are rather recent. The etymological note in the OED summarizes this odd history:
< Anglo-Norman nice, nis, nise and Old French nice (c1160; c1250 as niche; now French regional) <classical Latin nescius (see nescious adj.). Compare Old Occitan nesci (c1150; also attested as neci, nesi, nessi; Occitan neci), Spanish necio (1220–50), Catalan neci, nici (both 14th cent.), Portuguesenecio (14th cent.; 15th cent. as néscio), Italian nescio (1321), all in sense ‘foolish, simple, ignorant’.
The semantic development of this word from ‘foolish, silly’ to ‘pleasing’ is not paralleled in Latin or in the Romance languages. The precise sense development in English is unclear. New English Dictionary (OED first edition) (1906) s.v. notes that ‘in many examples from the 16th and 17th cent. it is difficult to say in what particular sense the writer intended it to be taken’.
A few entries show this change, with maybe a hint or two of what emerged in the sixteenth century might have transformed the senses of the word.
ADJECTIVE
1.a. c1300–1617
Of a person: foolish, silly, simple; ignorant. Obsolete.
1.b. a1393–1657
Of an action, utterance, etc.: displaying foolishness or silliness; absurd, senseless. Obsolete.
2.a. a1387–1665
Of conduct, behaviour, etc.: characterized by or encouraging wantonness or lasciviousness. Obsolete.
2.b. a1393–1605
Of a person: wanton, dissolute, lascivious. Obsolete.
Here we see the beginning of the shift:
2.c. 1395–1771
Of dress: extravagant, showy, ostentatious. Also in extended use. Obsolete.
2.d. c1400–1580
Of a person: finely dressed, elegant. Cf. Phrases P.3a. Obsolete.
3.a. c1387–
Precise or particular in matters of reputation or conduct; scrupulous, punctilious. Now rare.
3.b. c1400–
Fastidious, fussy, difficult to please, esp. with regard to food or cleanliness; of refined or dainty tastes.
3.c. 1584–1861
† Particular, strict, or careful with regard to a specific point or thing. Obsolete.
Now, in Shakespeare's era, we see the step toward our dominant modern sense:
3.d. 1588–
Refined, cultured; associated with polite society.
3.f. 1799–
Respectable, virtuous, decent.
3.g. 1863–
Of a topic of conversation, mode of conduct, etc.: in good taste, appropriate, proper. Usually in negative contexts.
4.a. a1393–1703
In early use: faint-hearted, timorous, cowardly. Later also: exhibiting qualities or characteristics regarded as feminine and inappropriate in a man (sometimes with the implication of homosexuality). Obsolete.
4.b. a1398–1604
Slothful, lazy, sluggish. Obsolete.
4.c. c1450–1813
Not able to endure much; tender, delicate, fragile. Obsolete.
4.d. 1621–1720
Pampered, luxurious. Obsolete. rare.
5. c1395–1703
† Strange, rare, extraordinary. Obsolete.
6.a. a1400–1823
Shy, coy, (affectedly) modest; reserved. Obsolete.
6.b. a1560–1699
Shy, reluctant, or unwilling in regard of or to. Also with in or infinitive. Obsolete.
7.a. ?a1500–
Not obvious or readily understood; difficult to decide or settle; demanding close consideration; †intricate (obsolete).
7.b. 1561–
Minute, subtle; (of differences) slight, small.
7.c. 1710–
Precise in correspondence; exact, closely judged.
8. a1522–
That requires or involves great precision or accuracy. Now rare.
9.a. 1567–1749
Slender, thin, fine; insubstantial. Obsolete.
9.b. a1594–1684
Unimportant, trivial. Obsolete.
Here we see our first hints of the modern shift.
10.a. 1589–1864
† That enters minutely into details; meticulous, attentive, sharp. Obsolete.
10.b. 1593–
Of the eye, ear, etc.: able to distinguish or discriminate to a high degree; sensitive, acute.
10.c. a1631–
Delicate or skilful in manipulation; dexterous. Also figurative.
10.d. 1697–
Of judgement, etc.: finely discriminative.
11.a. 1598–1822
Critical, doubtful; full of risk or uncertainty. Obsolete.
11.b. a1630–1858
Requiring tact, care, or discrimination in handling. Obsolete.
12.a. 1600–
Minutely or carefully accurate.
12.b. a1628–1875
† Of an instrument or apparatus: capable of showing minute differences; finely poised or adjusted. Obsolete.
13. 1709–
Of food or drink: dainty, choice; (later in weakened sense) tasty, appetizing; refreshing, restorative.
Only in the eighteenth century do we see our current dominant sense.
14.a. 1747–
That one derives pleasure or satisfaction from; agreeable, pleasant, satisfactory; attractive.
14.b. 1796–
Used as an intensifier with a predicative adjective or adverb in nice and ——, sometimes ironically.
14.c. 1797–
Of a person: pleasant in manner, agreeable, good-natured; attractive.
14.d. 1798–
Used ironically.
14.e. 1830–
Kind or considerate in behaviour; friendly (towards others). Frequently in to be nice (to).
14.f. 1850–
Of a (finished) action, task, etc.: well-executed; commendably performed or accomplished. Now frequently in interjections, as nice going!, nice try!, nice work!. Also used ironically or sarcastically.
14.g. 1970–
colloquial. nice one: expressing approval or congratulations for something done well. In later use also ironically.
Popularized by the song Nice One Cyril, used in a television commercial for bread in the early 1970s, and recorded in 1973 by the Tottenham Hotspur football team (associated with the former Tottenham player Cyril Knowles).
silly
This history is somewhat different. One of the original meanings, derived from its Germanic ancestor, has not been identified after 1825:
ADJECTIVE
I. † Senses relating to worthiness or blessedness.
I.1. Chiefly Scottish.
I.1.a. Worthy, good. Also: pious, holy. Cf. seely adj. 4. Obsolete. a1450–182
Its now almost utterly deceased relative seely, meaning blessed, pious, morally good, or innocent contains the tinge of meaning that now dominates silly. Here's the etymology:
Common West Germanic: Old English *sǽlig (implied in the synonymous gesǽlig i-seli adj., and in the adverb séliglíce seelily adv.) = Old Frisian sêlich (modern North Frisian salig, West Frisian sillich), Old Saxon sâlig, Middle Dutch sâlech (Dutch zalig), Old High German sâlig (Middle High Germansælic, modern German selig) < Germanic type *sǣligo- < *sǣli-z luck, happiness (Gothic sêls, Old English sǽl: see sele n.). In ordinary modern English the word is represented by silly adj., n., & adv., a form which arose in the 15th cent. from a shortening of the vowel, the pronunciation of which had changed from /eː/ to something approaching /iː/ .
If you listened to the Lexicon Valley podcast episode about the word business that I mentioned in last week's email, you'll have a sense of the sound changes we'll discuss more fully next week.
The German and Yiddish selig, or blessed is a cognate of this older form