EisheR, J.,
delivered the opinion of the court.
The defendant was sued in the Circuit Court of Monroe county, as guarantor of a promissory note made by one W. E. Holly, payable to the defendant, and by him indorsed to the plaintiff.
The indorsement, as it appears by the note in the record, is as follows: “ I indorse this note to Wyatt Moye, for value of him received, April 22d, 1851, and guarantee its payment.” Signed, Edward Herndon. The defendant pleaded under oath, that the words “ and guarantee its payment,” had been added to the in-dorsement without his knowledge or consent, after the delivery of the note to the plaintiff, and that the words constituting the indorsement as made by the defendant, had been retraced after such delivery with a pen. Issue being joined upon this plea, the jury found a verdict for the defendant. The plaintiff moved for a new trial, which was by the court below overruled, when the plaintiff took his bill of exceptions, embodying the evidence introduced on the trial, as well as the instructions asked by counsel, given and refused by the court.
It will at once be perceived that the main question for the jury to try was, whether the words constituting the guaranty had been added to the indorsement after the plaintiff came into possession of the note, as the other alteration was of itself wholly immaterial, except so far as it might serve to show a general uniformity in the entire writing, and thereby create the impression that it was all written by the same hand and at the same time. The signature of the defendant being admitted to the indorsement, the plaintiff’s coun*118sel contented himself by merely reading the note and indorsement to the jury in the first instance, and there resting his case. The defendant then introduced in regular order several witnesses, shilled as they each proved, in judging of various handwritings, and after inspecting the indorsement, each gave it as his opinion, that the letters constituting part of the indorsement had been retraced with a pen, and.that the words, “and guarantee its payment,” were written in ink of the same color as that used in retracing the letters. It is, however, unnecessary to set forth the evidence at large, as it is its competency and not -its sufficiency, that calls for our decision. The witnesses being wholly unacquainted with the handwriting of the parties, the question is, whether their testimony can be received, upon the principle that persons skilled in a particular science, may give their opinion touching matters connected therewith. Or, to employ the language in general use as applicable to the subject under consideration, was it competent to receive the opinions of experts, as to the alteration or additions alleged to have been made in and to this writing. In the case of Moody v. Rowell, 17 Pick. 493, the court, after a careful review of the principal authorities, held, that such evidence was competent, remarking at the same time, that it was agreed on all hands, that such evidence was in general deserving of little consideration; but as already remarked, it is the competency, and not the sufficiency of the evidence to produce conviction on the minds of the jury, upon which we are called to decide. The evidence being admitted, the presumption is, that the jury will give to it such weight, all the surrounding circumstances considered, as it ought to receive; that they will inspect the writing for themselves, and will at the same time determine, wherein they have been aided by the opinions of others professing greater skill than themselves in such matters; whether, in truth, the opinions of the witnesses are entitled to more weight than their own opinions, arising from an inspection of the writing; and finally, that if the writing does not disclose the alteration on its face, or is not different from the admitted or established handwriting of the party proven to have written it, that though the contract may have been materially altered, yet it is difficult for any evidence, resting merely upon the opinions of witnesses, *119to establish the fact beyond controversy. The most that can be attained by snob evidence is strong probability that tbe fact is so. These remarks, however, will be understood as applying more properly to those ingeniously executed counterfeits of writings, which carry upon their face at least a reasonable degree of the probability of their genuineness. If the writing itself be suspicious, it may require but very slight evidence to turn the scale; and a jury, though supposed to be versed in the affairs and business transactions of life, and though possessed of even more than ordinary intelligence, might not at the same time possess that peculiar skill, which would enable them to decide upon the face of the paper. It is the nature of man to acquire a certain degree of skill, in that which he has set out to learn, and which he has long pursued as a vocation. An eye practised in judging writings, may, at a glance, detect irregularities or counterfeits about it, which would entirely escape notice or detection from an unpractised eye. The rules of evidence should be so moulded, as to make it at least possible to detect every description of forgery or counterfeits; otherwise, only the clumsily executed ones, would ever meet with detection or condemnation. Adroitness in their execution, would in many cases insure success to those who might forge or alter written instruments. Both government and law presuppose human-weakness, and at least, the possibility of human depravity, and those connected with the administration of the law, know, perhaps from actual observation, that what is but a theory in government, is in many cases true as a fact. It is indeed part of the very law of evidence itself, that it will adapt its rules to every variety of case or question, which may arise for investigation in a court of justice. A clumsily executed counterfeit generally carries.,upon its face the evidence of its own condemnation. Not so, however;- with respect to one ingeniously executed. An unpractised eye, or unskilled person in writing, can derive but little, if any aid, from the writing, in forming an opinion in such a case. To shut out the evidence which might be afforded by skilful persons in the art of writing, would be almost equivalent to saying that the law had provided no means by which well executed forgeries or imitations could be detected, and they must therefore be respected as genuine *120instruments. Every such investigation involves more or less a question of fraud; and it bas long been an established rule, that courts would not hold themselves bound by any fixed definition of fraud, lest the ingenuity and artifice of dishonest men might devise means to evade the definition. The same may be said with respect to the rules of evidence in this class of cases. Narrow or contracted rules may enable persons of even tolerable skill to defy the scrutiny of a legal investigation, when under different rules detection would be certain.
It is believed, however, to be unnecessary to continue further the examination of this question. We believe the evidence offered by the defendant was competent, adopting at the same time the admonition of the Supreme Court of Massachusetts, that it ought to be received and weighed cautiously by the jury.
It is next assigned as error, that the court refused to give to the jury the following instruction, asked by the plaintiff’s counsel, to wit: That under the pleadings in this case, it devolves ©n the defendant to prove that the words, “and guarantee its payment,” on the back of the note, were placed there, without the knowledge or consent of Herndon, and unless this proof has been made, the jury must find for the plaintiff. This instruction, with slight modifications, might have been given, but it is made unnecessary by the fourth instruction, on behalf of the plaintiff, which the court gave, to wit: “If, in the opinion of the jury, there is no alteration apparent on the face of the paper sued on, then, under the issue in this case, it is incumbent on the defendant to show its existence by proof, and if he has failed to do so, they must find for the plaintiff.” This instruction, in our opinion, announces the law correctly, and rendered the other instruction, if not improper, at least unnecessary.
The last error which we will notice as assigned by counsel, consists in the following instruction, given on behalf of the counsel for the defendant, to wit: “ If the jury believe that an alteration in the indorsement was made, in a point 6 not’ material, fraudulently by the holder, they must find for the defendant.” We are of opinion that the court erred in giving this instruction. An immaterial alteration may be treated as no alteration. Perhaps *121under the English law, a different rule might with some, if not good reason, prevail, as all contracts which have been reduced to writing, must be stamped before they can be admitted in evidence, and the fraud spoken of, is a fraud not so much upon the party as upon the stamp laws, which are guarded with great vigilance by the government. But be this as it may, and conceding for the sake of the argument, that the instruction is sustained by respectable authority, yet we must be permitted to say, that the principle it announces is wrong. That which cannot by possibility work a change in the substantial part of the contract, cannot be said to be an alteration of it in a legal sense. If one party can receive no more than he was to receive under the terms of the contract, and the liability of the other remained the same as when he gave his consent to it, the change, whatever it may be, or may have been, cannot be said to be material, and if not material, it must be treated as nothing. If this position be true, the act cannot be the subject of a judicial investigation, and if the act itself be unimportant, upon what principle is it that the court can undertake to probe the motives of the party who committed it. If there be fraud at all in such a case, it can only be such as a bad motive can affix to an immaterial act, and if the act itself, is incapable of working an injury, to wit, of changing the rights or obligations of the parties to the contract, it cannot in a legal sense be said to be fraudulent, for the obvious reason that courts of justice only regard that as fraudulent, which is capable of producing an injury or loss to the other party to the controversy. Any other rule would simply amount to this: the defendant would say to the plaintiff, it is true your act was harmless, and amounted to nothing, but your motives were bad, and I therefore claim an exemption from my contract. It may be stated as a rule without exception, that when men’s acts cannot be the subject of judicial investigation, their motives cannot be inquired into. It was therefore, possible for this instruction to mislead the jury, as their minds may have been drawn away from the main question, to wit: the material alteration. It is not intended to intimate that the immaterial alteration was not competent evidence to go to the jury, to aid in the investigation of the main fact. The immaterial alterations may have been made. *122if at all, (about wbicb no opinion is intimated either way,) with a view of giving to tbe writing as a whole, the same general appearance, thereby making detection as to the material part, more difficult. Both acts and motives, when intended to aid in the establishment of the main fact, may be considered.
We are of opinion, for the reason above named, that the judgment ought to be reversed, and a new trial granted. The jury ought to be left to weigh the evidence, trammelled with as few instructions as possible, as there is really nothing but a pure question of fact involved.
Judgment reversed, and new trial granted.