(1) the prohibition of the individual lawyer’s representation is based on an interest of the lawyer described in Rule 1.7(b)(4) and that interest does not present a significant risk of adversely affecting the representation of the client by the remaining lawyers in the firm; or
(2) the representation is permitted by Rules 1.11, 1.12, or 1.18.
(b) When a lawyer becomes associated with a firm, the firm may not knowingly represent a person in a matter which is the same as, or substantially related to, a matter with respect to which the lawyer had previously represented a client whose interests are materially adverse to that person and about whom the lawyer has in fact acquired information protected by Rule 1.6 that is material to the matter. The firm is not disqualified if the lawyer participated in a previous representation or acquired information under the circumstances covered by Rule 1.6(h) or Rule 1.18.
(c) When a lawyer has terminated an association with a firm, the firm is not prohibited from thereafter representing a person with interests materially adverse to those of a client who was represented by the formerly associated lawyer during the association and is not currently represented by the firm, unless:
(1) the matter is the same or substantially related to that in which the formerly associated lawyer represented the client; and
(2) any lawyer remaining in the firm has information protected by Rule 1.6 that is material to the matter.
(d) A disqualification prescribed by this rule may be waived by the affected client under the conditions stated in Rule 1.7.
(e) A lawyer who, while affiliated with a firm, is made available to assist the Office of the Attorney General of the District of Columbia in providing legal services to that agency is not considered to be associated in a firm for purposes of paragraph (a), provided, however, that no such lawyer shall represent the Office of the Attorney General with respect to a matter in which the lawyer’s firm appears on behalf of an adversary.
Definition of “Firm”
 Whether two or more lawyers constitute a firm within this definition can depend on the specific facts. See Rule 1.0(c). For purposes of this rule, the term “firm” includes lawyers in a private firm and lawyers employed in the legal department of a corporation, legal services organization, or other organization, but does not include a government agency or other government entity. For example, two practitioners who share office space and occasionally consult or assist each other ordinarily would not be regarded as constituting a firm. However, if they present themselves to the public in a way suggesting that they are a firm or conduct themselves as a firm, they should be regarded as a firm for purposes of the Rules. The terms of any formal agreement between associated lawyers are relevant in determining whether they are a firm, as is the fact that they have mutual access to confidential information concerning the clients they serve. Furthermore, it is relevant in doubtful cases to consider the underlying purpose of the Rule that is involved. A group of lawyers could be regarded as a firm for purposes of the Rule that the same lawyer should not represent opposing parties in litigation, while it might not be so regarded for purposes of the Rule that information acquired by one lawyer is attributed to another.
 There is ordinarily no question that the members of the law department of an organization constitute a firm within the meaning of the Rules of Professional Conduct, but there can be uncertainty as to the identity of the client. For example, it may not be clear whether the law department of a corporation represents a subsidiary or an affiliated corporation, as well as the corporation by which the members of the department are directly employed. A similar question can arise concerning an unincorporated association and its local affiliates.
 Similar questions can also arise with respect to lawyers in legal aid organizations. Lawyers employed in the same unit of a legal service organization constitute a firm, but not necessarily those employed in separate units. As in the case of independent practitioners, whether the lawyers should be treated as associated with each other can depend on the particular Rule that is involved, and on the specific facts of the situation.
Principles of Imputed Disqualification
 The rule of imputed disqualification stated in paragraph (a) gives effect to the principle of loyalty to the client as it applies to lawyers who practice in a law firm. Such situations can be considered from the premise that a firm of lawyers is essentially one lawyer for purposes of the Rules governing loyalty to the client, or from the premise that each lawyer is vicariously bound by the obligation of loyalty owed by each lawyer with whom the lawyer is associated. Paragraph (a) operates only among the lawyers currently associated in a firm. When a lawyer moves from one firm to another, the situation is governed by paragraph (b) or (c).
 Where an individual lawyer is prohibited from engaging in certain transactions under Rule 1.8, paragraph (j) of that Rule, and not this Rule, governs whether that prohibition applies also to other lawyers in a firm with which that lawyer is associated. For issues involving prospective clients, see Rule 1.18.
 Where a lawyer has joined a private firm after having represented the government, the situation is governed by Rule 1.11.
 Different provisions are thus made for movement of a lawyer from one private firm to another and for movement of a lawyer from the government to a private firm. The government is entitled to protection of its client confidences, and therefore to the protections provided in Rules 1.6 and 1.11. Nevertheless, if the more extensive disqualification in Rule 1.10 were applied to former government lawyers, the potential effect on the government would be unduly burdensome. The government deals with all private citizens and organizations, and thus has a much wider circle of adverse legal interests than does any private law firm. In these circumstances, the government’s recruitment of lawyers would be seriously impaired if Rule 1.10 were applied to the government. On balance, therefore, the government is better served in the long run by the protections stated in Rule 1.11.
Exception for Personal Interest of the Disqualified Lawyer
 The rule in paragraph (a) does not prohibit representation by the firm where neither questions of client loyalty nor protection of confidential information are presented. Where an individual lawyer could not effectively represent a given client because of an interest described in Rule 1.7(b)(4), but that lawyer will do no work on the matter and the disqualifying interest of the lawyer will not adversely affect the representation by others in the firm, the firm should not be disqualified. For example, a lawyer’s strong political beliefs may disqualify the lawyer from representing a client, but the firm should not be disqualified if the lawyer’s beliefs will not adversely affect the representation by others in the firm. Similarly, representation of a client by the firm would not be precluded merely because the client’s adversary is a person with whom one of the firm’s lawyers has longstanding personal or social ties or is represented by a lawyer in another firm who is closely related to one of the firm’s lawyers. See Rule 1.7, Comment  and Rule 1.8(h), Comment , respectively. Nor would representation by the firm be precluded merely because one of its lawyers is seeking possible employment with an opponent (e.g., U.S. Attorney’s Office) or with a law firm representing the opponent of a firm client.
Lawyers Moving Between Firms
 When lawyers move between firms or when lawyers have been associated in a firm but then end their association, the fiction that the law firm is the same as a single lawyer is no longer wholly realistic. There are several competing considerations. First, the client previously represented must be reasonably assured that the principle of loyalty to the client is not compromised. Second, the rule of disqualification should not be so broadly cast as to preclude other persons from having reasonable choice of legal counsel. Third, the rule of disqualification should not unreasonably hamper lawyers from forming new associations and taking on new clients after having left a previous association, or unreasonably hamper the former firm from representing a client with interests adverse to those of a former client who was represented by a lawyer who has terminated an association with the firm. In this connection, it should be recognized that today many lawyers practice in firms, that many to some degree limit their practice to one field or another, and that many move from one association to another several times in their careers. If the concept of imputed disqualification were defined with unqualified rigor, the result would be radical curtailment of the opportunity of lawyers to move from one practice setting to another and of the opportunity of clients to change counsel.
 Reconciliation of these competing principles in the past has been attempted under two rubrics. One approach has been to seek per se rules of disqualification. For example, it has been held that a partner in a law firm is conclusively presumed to have access to all confidences concerning all clients of the firm. Under this analysis, if a lawyer has been a partner in one law firm and then becomes a partner in another law firm, there is a presumption that all confidences known by a partner in the first firm are known to all partners in the second firm. This presumption might properly be applied in some circumstances, especially where the client has been extensively represented, but may be unrealistic where the client was represented only for limited purposes. Furthermore, such a rigid rule exaggerates the difference between a partner and an associate in modern law firms.
 The other rubric formerly used for dealing with vicarious disqualification is the appearance of impropriety proscribed in Canon 9 of the Code of Professional Responsibility. Applying this rubric presents two problems. First, the appearance of impropriety can be taken to include any new client lawyer relationship that might make a former client feel anxious. If that meaning were adopted, disqualification would become little more than a question of subjective judgment by the former client. Second, since “impropriety” is undefined, the term “appearance of impropriety” is question-begging. It therefore has to be recognized that the problem of imputed disqualification cannot be properly resolved either by simple analogy to a lawyer practicing alone or by the very general concept of appearance of impropriety.
 A rule based on a functional analysis is more appropriate for determining the question of vicarious disqualification. Two functions are involved: preserving confidentiality and avoiding positions adverse to a client.
 Preserving confidentiality is a question of access to information. Access to information, in turn, is essentially a question of fact in particular circumstances, aided by inferences, deductions, or working presumptions that reasonably may be made about the way in which lawyers work together. A lawyer may have general access to files of all clients of a law firm and may regularly participate in discussions of their affairs; it should be inferred that such a lawyer in fact is privy to all information about all the firm’s clients. In contrast, another lawyer may have access to the files of only a limited number of clients and participate in discussion of the affairs of no other clients; in the absence of information to the contrary, it should be inferred that such a lawyer in fact is privy to information about the clients actually served but not those of other clients.
 Application of paragraphs (b) and (c) depends on a situation’s particular facts. In any such inquiry, the burden of proof should rest upon the firm whose disqualification is sought.
 The provisions of paragraphs (b) and (c) which refer to possession of protected information operate to disqualify the firm only when the lawyer involved has actual knowledge of information protected by Rule 1.6. Thus, if a lawyer while with one firm acquired no knowledge of information relating to a particular client of the firm, and that lawyer later joined another firm, neither the lawyer individually nor the second firm is disqualified from representing another client in the same or a substantially related matter even though the interests of the two clients conflict.
 Independent of the question of disqualification of a firm, a lawyer changing professional association has a continuing duty to preserve confidentiality of information about a client formerly represented. See Rule 1.6.
 The second aspect of loyalty to a client is the lawyer’s obligation to decline subsequent representations involving positions adverse to a former client arising in the same or substantially related matters. This obligation requires abstention from adverse representations by the individual lawyer involved, and may also entail abstention of other lawyers through imputed disqualification. Hence, this aspect of the problem is governed by the principles of Rule 1.9. Thus, under paragraph (b), if a lawyer left one firm for another, the new affiliation would preclude the lawyer’s new firm from continuing to represent clients with interests materially adverse to those of the lawyer’s former clients in the same or substantially related matters. In this respect paragraph (b) is at odds with – and thus must be understood to reject – the dicta expressed in the “second” hypothetical in the second paragraph of footnote 5 of Brown v. District of Columbia Board of Zoning Adjustment, 486 A.2d 37, 42 n. 5 (D.C. 1984) (en banc), premised on LaSalle National Bank v. County of Lake, 703 F.2d 252, 257-59 (7th Cir. 1983).
 The concept of “former client” as used in paragraph (b) extends only to actual representation of the client by the newly affiliated lawyer while that lawyer was employed by the former firm. Thus, not all of the clients of the former firm during the newly affiliated lawyer’s practice there are necessarily deemed former clients of the newly affiliated lawyer. Only those clients with whom the newly affiliated lawyer in fact personally had a lawyer client relationship are former clients within the terms of paragraph (b).
 The last sentence of paragraph (b) limits the imputation rule in certain limited circumstances. Those circumstances involve situations in which any secrets or confidences obtained were received before the lawyer had become a member of the Bar, but during a time when such person was providing assistance to another lawyer. The typical situation is that of the part time or summer law clerk, or so called summer associate. Other types of assistance to a lawyer, such as working as a paralegal or legal assistant, could also fall within the scope of this sentence. The limitation on the imputation rule is similar to the provision dealing with judicial law clerks under Rule 1.11(b). Not applying the imputation rule reflects a policy choice that imputation in such circumstances could unduly impair the mobility of persons employed in such nonlawyer positions once they become members of the Bar. The personal disqualification of the former non-lawyer is not affected, and the lawyer who previously held the non-legal job may not be involved in any representation with respect to which the firm would have been disqualified but for the last sentence of paragraph (b). Rule 1.6(h) provides that the former nonlawyer is subject to the requirements of Rule 1.6 (regarding protection of client confidences and secrets) just as if the person had been a member of the Bar when employed in the prior position.
 Under certain circumstances, paragraph (c) permits a law firm to represent a person with interests directly adverse to those of a client represented by a lawyer who formerly was associated with the firm. The Rule applies regardless of when the formerly associated lawyer represented the client. The firm, however, may not represent a person in a matter adverse to a current client of the firm, which would violate Rule 1.7. Moreover, the firm may not represent the person where the matter is the same as, or substantially related to, that in which the formerly associated lawyer represented the client and any other lawyer currently in the firm has material information protected by Rule 1.6.
Lawyers Assisting the Office of the Attorney General of the District
 The Office of the Attorney General of the District of Columbia may experience periods of peak need for legal services which cannot be met by normal hiring programs, or may experience problems in dealing with a large backlog of matters requiring legal services. In such circumstances, the public interest is served by permitting private firms to provide the services of lawyers affiliated with such private firms on a temporary basis to assist the Office of the Attorney General. Such arrangements do not fit within the classical pattern of situations involving the general imputation rule of paragraph (a). Provided that safeguards are in place which preclude the improper disclosure of client confidences or secrets, and the improper use of one client’s confidences or secrets on behalf of another client, the public interest benefits of such arrangements justify an exception to the general imputation rule, just as Comment  excludes from the definition of “firm” lawyers employed by a government agency or other government entity. Lawyers assigned to assist the Office of the Attorney General pursuant to such temporary programs are, by virtue of paragraph (e), treated as if they were employed as government employees and as if their affiliation with the private firm did not exist during the period of temporary service with the Office of the Attorney General. See Rule 1.11(h) with respect to the procedures to be followed by lawyers participating in such temporary programs and by the firms with which such lawyers are affiliated after the participating lawyers have ended their participation in such temporary programs.
 The term “made available to assist the Office of the Attorney General in providing legal services” in paragraph (e) contemplates the temporary cessation of practice with the firm during the period legal services are being made available to the Office of the Attorney General, so that during that period the lawyer’s activities which involve the practice of law are devoted fully to assisting the Office of the Attorney General.
 Rule 1.10(e) prohibits a lawyer who is assisting the Office of the Attorney General from representing that office in any matter in which the lawyer’s firm represents an adversary. Rule 1.10(e) does not, however, by its terms, prohibit lawyers assisting the Office of the Attorney General from participating in every matter in which the Attorney General is taking a position adverse to that of a current client of the firm with which the participating lawyer was affiliated prior to joining the program of assistance to the Office of the Attorney General. Such an unequivocal prohibition would be overly broad, difficult to administer in practice, and inconsistent with the purposes of Rule 1.10(e).
 The absence of such a per se prohibition in Rule 1.10(e) does not diminish the importance of a thoughtful and restrained approach to defining those matters in which it is appropriate for a participating lawyer to be involved. An appearance of impropriety in programs of this kind can undermine the public’s acceptance of the program and embarrass the Office of the Attorney General, the participating lawyer, that lawyer’s law firm and clients of that firm. For example, it would not be appropriate for a participant lawyer to engage in a representation adverse to a party who is known to be a major client of the participating lawyer’s firm, even though the subject matter of the representation of the Office of the Attorney General bears no substantial relationship to any representation of that party by the participating lawyer’s firm. Similarly, it would be inappropriate for a participating lawyer to be involved in a representation adverse to a party that the participating lawyer has been personally involved in representing while at the firm, even if the client is not a major client of the firm. The appropriate test is that of conservative good judgment; if any reasonable doubts concerning the unrestrained vigor of the participating lawyer’s representation on behalf of the Office of the Attorney General might be created, the lawyer should advise the appropriate officials of the Office of the Attorney General and decline to participate. Similarly, if participation on behalf of the Office of the Attorney General might reasonably give rise to a concern on the part of a participating lawyer’s firm or a client of the firm that its secrets or confidences (as defined by Rule 1.6) might be compromised, participation should be declined. It is not anticipated that situations suggesting the appropriateness of a refusal to participate will occur so frequently as to significantly impair the usefulness of the program of participation by lawyers from private firms.
 The primary responsibility for identifying situations in which representation by the participating lawyer might raise reasonable doubts as to the lawyer’s zealous representation on behalf of the Office of the Attorney General must rest on the participating lawyer, who will generally be privy to nonpublic information bearing on the appropriateness of the lawyer’s participation in a matter on behalf of the Office of the Attorney General. Recognizing that many representations by law firms are nonpublic matters, the existence and nature of which may not be disclosed consistent with Rule 1.6, it is not anticipated that law firms from which participating lawyers have been drawn would be asked to perform formal “conflicts checks” with respect to matters in which participating lawyers may be involved. However, consultations between participating lawyers and their law firms to identify potential areas of concern, provided that such consultations honor the requirements of Rule 1.6, are appropriate to protect the interests of all involved – the Office of the Attorney General, the participating lawyer, that lawyer’s law firm and any clients whose interests are potentially implicated.