Allen and Greenough's New Latin Grammar, section 398

Heavy Construction

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ABLATIVE CASE.

398.

Under the name Ablative are included the meanings and, In part, the forms of three cases, - the Ablative proper, expressing the relation FROM; the Locative, IN; and the Instrumental, WITH or BY. These three cases were originally not wholly distinct in meaning, and their confusion was rendered more certain (1) by the development of meanings that approached each other and (2) by phonetic decay, by means of which these cases have become largely identical in form. Compare, for the first, the phrases á parte dexterá, ON the right, quam ob causam, FROM which cause; ad famam, AT (in consequence of) the report; and, for the second, the like forms of the dative and ablative plural, the old dative in -é of the fifth declension (§96), and the loss of the original -d of the ablative (§49. e; cf. §§43. N. 1, 92.f, 214. a. N.).

The relation of FROM includes separation, source, cause, agent, and comparison; that of WITH or BY, accompaniment, instrument, means, manner, quality, and price; that of IN or AT, place, time, circumstance. This classification according to the original cases (to which, however, too great a degree of certainty should not be attached)[1][Thus the Ablative of Cause may be, at least in part, of Instrumental origin, and the Ablative Absolute appears to combine the Instrumental and the Locative.] is set forth in the following table: -

I. Ablative Proper (from) 1. Of Separation, Privation, and Want (§400).
(Separative): 2. Of Source (participles of origin, etc.) (§403).
3. Of Cause (labóró, exsilió, etc.) (§404).
4. Of Agent (with ab after Passives) (§405).
5. Of Comparison (THAN) (§406).

II. Instrumental Ablative
1. Of Manner, Means, and Instrument(§408 ff.).
(with): 2. Of Object of the Deponents útor etc.(§410).
3. Of Accompaniment (with cum) (§413).
4. Of Degree of Difference (§414).
5. Of Quality (with Adjectives) (§415).
6. Of Price and Exchange (§416).
7. Of Specification (§418).
8. Ablative Absolute (§419).

III. Locative Ablative
1. Of Place where (commonly with in) (§421)
(in, on, at): 2. Of Time and Circumstance (§423)

*I. Ablative Proper (from)*	1.	Of Separation, Privation, and Want (§400).
*(Separative):*	2.	Of Source (participles of origin, etc.) (§403).
	3.	Of Cause (labóró, exsilió, etc.) (§404).
	4.	Of Agent (with ab after Passives) (§405).
	5.	Of Comparison (THAN) (§406).
II. Instrumental Ablative	1.	Of Manner, Means, and Instrument(§408 ff.).
*(with):*	2.	Of Object of the Deponents útor etc.(§410).
	3.	Of Accompaniment (with cum) (§413).
	4.	Of Degree of Difference (§414).
	5.	Of Quality (with Adjectives) (§415).
	6.	Of Price and Exchange (§416).
	7.	Of Specification (§418).
	8.	Ablative Absolute (§419).
III. Locative Ablative	1.	Of Place where (commonly with in) (§421)
*(in, on, at):*	2.	Of Time and Circumstance (§423)