The liability incurred by a surety under his guarantee depends upon its terms, and is not necessarily co-extensive with that of the principal debtor. It is, however, obvious that as the surety's obligation is merely accessory to that of the principal it cannot as such exceed it (de Colyar, _Law of Guarantees_, 3rd ed. p. 233; Burge, _Suretyship_, p. 5). By the Roman law, if there were any such excess the surety's obligation was rendered _wholly_ void and not merely void _pro tanto_. By many existing codes civil, however, a guarantee which imposes on the surety a greater liability than that of the principal is not thereby invalidated, but the liability is merely reducible to that of the principal (Fr. and Bel. 2013; Port. 823; Spain, 1826; Italy, 1900; Holland, 1859; Lower Canada, 1933). By sec. 128 of the Indian Contract Act 1872 the liability of the surety is, unless otherwise provided by contract, coextensive with that of the principal. Where the liability of the surety is _less_ extensive in amount than that of the principal debtor, difficult questions have arisen in England and America as to whether the surety is liable only for _part_ of the debt equal to the limit of his liability, or, up to such limit, for the _whole_ debt (_Ellis_ v. _Emmanuel_, 1 Ex. Div. 157; _Hobson_ v. _Bass_, 6 Ch. App. 792; Brandt, _Suretyship_, sec. 219). The surety cannot be made liable except for a loss sustained by reason of the default guaranteed against. Moreover, in the case of a joint and several guarantee by several sureties, unless all sign it none are liable thereunder (_National Pro. Bk. of England_ v. _Brackenbury_, 1906, 22 _Times_ L.R. 797). It was formerly considered in England to be the duty of the party taking a guarantee to see that it was couched in language enabling the party giving it to understand clearly to what extent he was binding himself (_Nicholson_ v. _Paget_, 1 C. & M. 48, 52). This view, however, can no longer be sustained, it being now recognized that a guarantee, like any other contract, must, in cases of ambiguity, be construed against the party bound thereby and in favour of the party receiving it (_Mayer_ v. _Isaac_, 6 M. & W. 605, 612; _Wood_ v. _Priestner_, L.R. 2 Exch. 66, 71). The surety is not to be changed beyond the limits prescribed by his contract, which must be construed so as to give effect to what may fairly be inferred to have been the intention of the parties, from what they themselves have expressed in writing. In cases of doubtful import, recourse to parol evidence is permissible, to explain, but not to contradict, the written evidence of the guarantee. As a general rule, the surety is not liable if the principal debt cannot be enforced, because, as already explained, the obligation of the surety is merely accessory to that of the principal debtor. It has never been actually decided in England whether this rule holds good in cases where the principal debtor is an infant, and on that account is not liable to the